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 $123.46   8.224%   $133.6134   $133.61   $133.60   $133.60  
  Purchase #2 $5.50   9.870%   $6.0429   $6.04   $6.05   $6.00  
  Purchase #3 $68.46   6.155%   $72.6737   $72.67   $72.65   $72.70  
  Purchase #4 $200.97   5.114%   $211.2476   $211.25   $211.25   $211.20  
  Purchase #5 $26.35   4.334%   $27.492   $27.49   $27.50   $27.50  
  Purchase #6 $190.40   6.180%   $202.1667   $202.17   $202.15   $202.20  
  Purchase #7 $90.73   5.481%   $95.7029   $95.70   $95.70   $95.70  
  7 purchase totals = $705.87       $748.9392   $748.93   $748.90   $748.90