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 $87.43   12.449%   $98.3142   $98.31   $98.30   $98.30  
  Purchase #2 $178.88   12.376%   $201.0182   $201.02   $201.00   $201.00  
  Purchase #3 $64.61   4.150%   $67.2913   $67.29   $67.30   $67.30  
  Purchase #4 $84.65   3.149%   $87.3156   $87.32   $87.30   $87.30  
  Purchase #5 $235.43   11.731%   $263.0483   $263.05   $263.05   $263.00  
  Purchase #6 $136.66   3.815%   $141.8736   $141.87   $141.85   $141.90  
  Purchase #7 $100.47   3.732%   $104.2195   $104.22   $104.20   $104.20  
  7 purchase totals = $888.13       $963.0807   $963.08   $963.00   $963.00