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 $47.38   11.727%   $52.9363   $52.94   $52.95   $52.90  
  Purchase #2 $119.62   11.654%   $133.5605   $133.56   $133.55   $133.60  
  Purchase #3 $62.51   7.108%   $66.9532   $66.95   $66.95   $67.00  
  Purchase #4 $197.94   9.597%   $216.9363   $216.94   $216.95   $216.90  
  Purchase #5 $166.84   13.369%   $189.1448   $189.14   $189.15   $189.10  
  Purchase #6 $44.38   12.503%   $49.9288   $49.93   $49.95   $49.90  
  Purchase #7 $225.97   12.687%   $254.6388   $254.64   $254.65   $254.60  
  7 purchase totals = $864.64       $964.0987   $964.10   $964.15   $964.00