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 $67.39   8.697%   $73.2509   $73.25   $73.25   $73.30  
  Purchase #2 $24.45   7.403%   $26.26   $26.26   $26.25   $26.30  
  Purchase #3 $121.47   5.740%   $128.4424   $128.44   $128.45   $128.40  
  Purchase #4 $51.30   4.127%   $53.4172   $53.42   $53.40   $53.40  
  Purchase #5 $232.38   3.316%   $240.0857   $240.09   $240.10   $240.10  
  Purchase #6 $154.57   13.596%   $175.5853   $175.59   $175.60   $175.60  
  Purchase #7 $249.46   3.104%   $257.2032   $257.20   $257.20   $257.20  
  7 purchase totals = $901.02       $954.2447   $954.25   $954.25   $954.30