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 $228.74   7.562%   $246.0373   $246.04   $246.05   $246.00  
  Purchase #2 $208.97   10.375%   $230.6506   $230.65   $230.65   $230.70  
  Purchase #3 $45.48   11.595%   $50.7534   $50.75   $50.75   $50.80  
  Purchase #4 $10.32   12.433%   $11.6031   $11.60   $11.60   $11.60  
  Purchase #5 $83.84   13.742%   $95.3613   $95.36   $95.35   $95.40  
  Purchase #6 $86.41   10.578%   $95.5504   $95.55   $95.55   $95.60  
  Purchase #7 $90.75   13.434%   $102.9414   $102.94   $102.95   $102.90  
  7 purchase totals = $754.51       $832.8975   $832.89   $832.90   $833.00