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 $250.86   4.830%   $262.9765   $262.98   $263.00   $263.00  
  Purchase #2 $51.66   13.807%   $58.7927   $58.79   $58.80   $58.80  
  Purchase #3 $201.83   10.520%   $223.0625   $223.06   $223.05   $223.10  
  Purchase #4 $90.73   10.281%   $100.058   $100.06   $100.05   $100.10  
  Purchase #5 $165.80   13.723%   $188.5527   $188.55   $188.55   $188.60  
  Purchase #6 $95.26   9.539%   $104.3469   $104.35   $104.35   $104.30  
  Purchase #7 $14.94   13.741%   $16.9929   $16.99   $17.00   $17.00  
  7 purchase totals = $871.08       $954.7822   $954.78   $954.80   $954.90