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 $65.32   5.122%   $68.6657   $68.67   $68.65   $68.70  
  Purchase #2 $64.52   6.227%   $68.5377   $68.54   $68.55   $68.50  
  Purchase #3 $11.51   6.605%   $12.2702   $12.27   $12.25   $12.30  
  Purchase #4 $228.37   13.105%   $258.2979   $258.30   $258.30   $258.30  
  Purchase #5 $95.52   13.422%   $108.3407   $108.34   $108.35   $108.30  
  Purchase #6 $247.70   7.603%   $266.5326   $266.53   $266.55   $266.50  
  Purchase #7 $63.31   7.534%   $68.0798   $68.08   $68.10   $68.10  
  7 purchase totals = $776.25       $850.7246   $850.73   $850.75   $850.70