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 $90.71   5.547%   $95.7417   $95.74   $95.75   $95.70  
  Purchase #2 $182.73   9.643%   $200.3507   $200.35   $200.35   $200.40  
  Purchase #3 $50.47   6.588%   $53.795   $53.80   $53.80   $53.80  
  Purchase #4 $81.28   10.373%   $89.7112   $89.71   $89.70   $89.70  
  Purchase #5 $111.54   7.218%   $119.591   $119.59   $119.60   $119.60  
  Purchase #6 $16.41   9.593%   $17.9842   $17.98   $18.00   $18.00  
  Purchase #7 $228.34   13.437%   $259.022   $259.02   $259.00   $259.00  
  7 purchase totals = $761.48       $836.1958   $836.19   $836.20   $836.20