Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.91   5.632%   $216.4505   $216.45   $216.45   $216.50  
  Purchase #2 $125.25   11.150%   $139.2154   $139.22   $139.20   $139.20  
  Purchase #3 $169.90   3.114%   $175.1907   $175.19   $175.20   $175.20  
  Purchase #4 $218.68   10.500%   $241.6414   $241.64   $241.65   $241.60  
  Purchase #5 $199.99   11.142%   $222.2729   $222.27   $222.25   $222.30  
  Purchase #6 $234.85   8.708%   $255.3007   $255.30   $255.30   $255.30  
  Purchase #7 $218.41   11.811%   $244.2064   $244.21   $244.20   $244.20  
  7 purchase totals = $1,371.99       $1,494.2780   $1,494.28   $1,494.25   $1,494.30