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 $121.72   11.154%   $135.2966   $135.30   $135.30   $135.30  
  Purchase #2 $205.78   6.604%   $219.3697   $219.37   $219.35   $219.40  
  Purchase #3 $178.49   10.557%   $197.3332   $197.33   $197.35   $197.30  
  Purchase #4 $65.64   10.489%   $72.525   $72.53   $72.55   $72.50  
  Purchase #5 $106.95   13.571%   $121.4642   $121.46   $121.45   $121.50  
  Purchase #6 $162.64   12.415%   $182.8318   $182.83   $182.85   $182.80  
  Purchase #7 $18.31   12.223%   $20.548   $20.55   $20.55   $20.50  
  7 purchase totals = $859.53       $949.3685   $949.37   $949.40   $949.30