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 $216.71   13.534%   $246.0395   $246.04   $246.05   $246.00  
  Purchase #2 $99.66   11.454%   $111.0751   $111.08   $111.10   $111.10  
  Purchase #3 $104.27   11.315%   $116.0682   $116.07   $116.05   $116.10  
  Purchase #4 $34.35   7.250%   $36.8404   $36.84   $36.85   $36.80  
  Purchase #5 $69.90   8.315%   $75.7122   $75.71   $75.70   $75.70  
  Purchase #6 $190.93   13.108%   $215.9571   $215.96   $215.95   $216.00  
  Purchase #7 $156.65   3.121%   $161.539   $161.54   $161.55   $161.50  
  7 purchase totals = $872.47       $963.2315   $963.24   $963.25   $963.20