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 $249.49   7.670%   $268.6259   $268.63   $268.65   $268.60  
  Purchase #2 $58.76   12.183%   $65.9187   $65.92   $65.90   $65.90  
  Purchase #3 $65.88   13.269%   $74.6216   $74.62   $74.60   $74.60  
  Purchase #4 $141.36   10.621%   $156.3738   $156.37   $156.35   $156.40  
  Purchase #5 $48.95   11.596%   $54.6262   $54.63   $54.65   $54.60  
  Purchase #6 $233.59   5.336%   $246.0544   $246.05   $246.05   $246.10  
  Purchase #7 $155.86   9.819%   $171.1639   $171.16   $171.15   $171.20  
  7 purchase totals = $953.89       $1,037.3845   $1,037.38   $1,037.35   $1,037.40