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 $33.77   8.471%   $36.6307   $36.63   $36.65   $36.60  
  Purchase #2 $65.63   6.190%   $69.6925   $69.69   $69.70   $69.70  
  Purchase #3 $70.57   4.688%   $73.8783   $73.88   $73.90   $73.90  
  Purchase #4 $204.53   5.534%   $215.8487   $215.85   $215.85   $215.80  
  Purchase #5 $48.79   4.632%   $51.05   $51.05   $51.05   $51.10  
  Purchase #6 $48.78   3.210%   $50.3458   $50.35   $50.35   $50.30  
  Purchase #7 $233.59   8.625%   $253.7371   $253.74   $253.75   $253.70  
  7 purchase totals = $705.66       $751.1831   $751.19   $751.25   $751.10