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 $42.82   4.201%   $44.6189   $44.62   $44.60   $44.60  
  Purchase #2 $131.93   4.395%   $137.7283   $137.73   $137.75   $137.70  
  Purchase #3 $25.36   8.405%   $27.4915   $27.49   $27.50   $27.50  
  Purchase #4 $124.46   6.450%   $132.4877   $132.49   $132.50   $132.50  
  Purchase #5 $69.98   4.743%   $73.2992   $73.30   $73.30   $73.30  
  Purchase #6 $247.41   6.616%   $263.7786   $263.78   $263.80   $263.80  
  Purchase #7 $85.36   9.676%   $93.6194   $93.62   $93.60   $93.60  
  7 purchase totals = $727.32       $773.0236   $773.03   $773.05   $773.00