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 $59.54   11.204%   $66.2109   $66.21   $66.20   $66.20  
  Purchase #2 $231.47   6.494%   $246.5017   $246.50   $246.50   $246.50  
  Purchase #3 $236.35   11.866%   $264.3953   $264.40   $264.40   $264.40  
  Purchase #4 $53.65   9.535%   $58.7655   $58.77   $58.75   $58.80  
  Purchase #5 $177.77   4.288%   $185.3928   $185.39   $185.40   $185.40  
  Purchase #6 $15.25   11.327%   $16.9774   $16.98   $17.00   $17.00  
  Purchase #7 $44.57   8.254%   $48.2488   $48.25   $48.25   $48.20  
  7 purchase totals = $818.60       $886.4924   $886.50   $886.50   $886.50