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 $93.80   3.552%   $97.1318   $97.13   $97.15   $97.10  
  Purchase #2 $60.84   5.739%   $64.3316   $64.33   $64.35   $64.30  
  Purchase #3 $175.82   12.472%   $197.7483   $197.75   $197.75   $197.70  
  Purchase #4 $230.36   8.318%   $249.5213   $249.52   $249.50   $249.50  
  Purchase #5 $230.55   8.869%   $250.9975   $251.00   $251.00   $251.00  
  Purchase #6 $149.39   10.351%   $164.8534   $164.85   $164.85   $164.90  
  Purchase #7 $175.98   11.387%   $196.0188   $196.02   $196.00   $196.00  
  7 purchase totals = $1,116.74       $1,220.6027   $1,220.60   $1,220.60   $1,220.50