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 $50.52   4.145%   $52.6141   $52.61   $52.60   $52.60  
  Purchase #2 $215.38   5.144%   $226.4591   $226.46   $226.45   $226.50  
  Purchase #3 $51.32   11.767%   $57.3588   $57.36   $57.35   $57.40  
  Purchase #4 $125.74   6.357%   $133.7333   $133.73   $133.75   $133.70  
  Purchase #5 $154.63   8.367%   $167.5679   $167.57   $167.55   $167.60  
  Purchase #6 $23.97   11.387%   $26.6995   $26.70   $26.70   $26.70  
  Purchase #7 $187.25   5.232%   $197.0469   $197.05   $197.05   $197.00  
  7 purchase totals = $808.81       $861.4796   $861.48   $861.45   $861.50