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 $54.81   6.322%   $58.2751   $58.28   $58.30   $58.30  
  Purchase #2 $156.58   3.477%   $162.0243   $162.02   $162.00   $162.00  
  Purchase #3 $148.42   4.733%   $155.4447   $155.44   $155.45   $155.40  
  Purchase #4 $191.29   11.565%   $213.4127   $213.41   $213.40   $213.40  
  Purchase #5 $66.32   12.129%   $74.364   $74.36   $74.35   $74.40  
  Purchase #6 $202.87   12.363%   $227.9508   $227.95   $227.95   $228.00  
  Purchase #7 $116.75   13.375%   $132.3653   $132.37   $132.35   $132.40  
  7 purchase totals = $937.04       $1,023.8369   $1,023.83   $1,023.80   $1,023.90