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 $168.99   8.444%   $183.2595   $183.26   $183.25   $183.30  
  Purchase #2 $59.85   11.226%   $66.5688   $66.57   $66.55   $66.60  
  Purchase #3 $185.30   8.809%   $201.6231   $201.62   $201.60   $201.60  
  Purchase #4 $137.30   7.857%   $148.0877   $148.09   $148.10   $148.10  
  Purchase #5 $181.63   12.621%   $204.5535   $204.55   $204.55   $204.60  
  Purchase #6 $37.97   3.743%   $39.3912   $39.39   $39.40   $39.40  
  Purchase #7 $156.93   6.550%   $167.2089   $167.21   $167.20   $167.20  
  7 purchase totals = $927.97       $1,010.6927   $1,010.69   $1,010.65   $1,010.80