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 $51.57   13.159%   $58.3561   $58.36   $58.35   $58.40  
  Purchase #2 $216.39   12.419%   $243.2635   $243.26   $243.25   $243.30  
  Purchase #3 $15.74   3.418%   $16.278   $16.28   $16.30   $16.30  
  Purchase #4 $46.37   9.757%   $50.8943   $50.89   $50.90   $50.90  
  Purchase #5 $180.51   8.657%   $196.1368   $196.14   $196.15   $196.10  
  Purchase #6 $187.70   3.849%   $194.9246   $194.92   $194.90   $194.90  
  Purchase #7 $236.48   5.588%   $249.6945   $249.69   $249.70   $249.70  
  7 purchase totals = $934.76       $1,009.5478   $1,009.54   $1,009.55   $1,009.60