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 $62.64   3.190%   $64.6382   $64.64   $64.65   $64.60  
  Purchase #2 $91.27   7.340%   $97.9692   $97.97   $97.95   $98.00  
  Purchase #3 $230.39   8.119%   $249.0954   $249.10   $249.10   $249.10  
  Purchase #4 $249.51   9.439%   $273.0612   $273.06   $273.05   $273.10  
  Purchase #5 $45.80   13.501%   $51.9835   $51.98   $52.00   $52.00  
  Purchase #6 $201.79   13.186%   $228.398   $228.40   $228.40   $228.40  
  Purchase #7 $28.64   10.671%   $31.6962   $31.70   $31.70   $31.70  
  7 purchase totals = $910.04       $996.8417   $996.85   $996.85   $996.90