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 $68.58   12.282%   $77.003   $77.00   $77.00   $77.00  
  Purchase #2 $46.94   3.833%   $48.7392   $48.74   $48.75   $48.70  
  Purchase #3 $97.90   4.331%   $102.14   $102.14   $102.15   $102.10  
  Purchase #4 $202.26   7.772%   $217.9796   $217.98   $218.00   $218.00  
  Purchase #5 $225.88   11.286%   $251.3728   $251.37   $251.35   $251.40  
  Purchase #6 $51.37   7.728%   $55.3399   $55.34   $55.35   $55.30  
  Purchase #7 $12.41   8.868%   $13.5105   $13.51   $13.50   $13.50  
  7 purchase totals = $705.34       $766.0850   $766.08   $766.10   $766.00