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 $130.69   12.438%   $146.9452   $146.95   $146.95   $146.90  
  Purchase #2 $84.95   8.729%   $92.3653   $92.37   $92.35   $92.40  
  Purchase #3 $156.95   3.386%   $162.2643   $162.26   $162.25   $162.30  
  Purchase #4 $24.88   6.320%   $26.4524   $26.45   $26.45   $26.50  
  Purchase #5 $250.57   5.696%   $264.8425   $264.84   $264.85   $264.80  
  Purchase #6 $19.55   3.649%   $20.2634   $20.26   $20.25   $20.30  
  Purchase #7 $63.96   6.468%   $68.0969   $68.10   $68.10   $68.10  
  7 purchase totals = $731.55       $781.2300   $781.23   $781.20   $781.30