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 $240.45   5.625%   $253.9753   $253.98   $254.00   $254.00  
  Purchase #2 $229.48   7.110%   $245.796   $245.80   $245.80   $245.80  
  Purchase #3 $162.84   10.589%   $180.0831   $180.08   $180.10   $180.10  
  Purchase #4 $16.29   7.766%   $17.5551   $17.56   $17.55   $17.60  
  Purchase #5 $120.80   10.192%   $133.1119   $133.11   $133.10   $133.10  
  Purchase #6 $52.49   10.609%   $58.0587   $58.06   $58.05   $58.10  
  Purchase #7 $13.69   3.650%   $14.1897   $14.19   $14.20   $14.20  
  7 purchase totals = $836.04       $902.7698   $902.78   $902.80   $902.90