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 $236.28   12.565%   $265.9686   $265.97   $265.95   $266.00  
  Purchase #2 $48.91   6.867%   $52.2686   $52.27   $52.25   $52.30  
  Purchase #3 $167.77   3.240%   $173.2057   $173.21   $173.20   $173.20  
  Purchase #4 $151.60   9.766%   $166.4053   $166.41   $166.40   $166.40  
  Purchase #5 $117.88   11.698%   $131.6696   $131.67   $131.65   $131.70  
  Purchase #6 $93.94   13.161%   $106.3034   $106.30   $106.30   $106.30  
  Purchase #7 $40.81   8.782%   $44.3939   $44.39   $44.40   $44.40  
  7 purchase totals = $857.19       $940.2151   $940.22   $940.15   $940.30