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 $205.55   3.219%   $212.1667   $212.17   $212.15   $212.20  
  Purchase #2 $112.83   8.709%   $122.6564   $122.66   $122.65   $122.70  
  Purchase #3 $202.56   9.213%   $221.2219   $221.22   $221.20   $221.20  
  Purchase #4 $219.68   4.595%   $229.7743   $229.77   $229.75   $229.80  
  Purchase #5 $206.88   5.314%   $217.8736   $217.87   $217.85   $217.90  
  Purchase #6 $163.47   8.559%   $177.4614   $177.46   $177.45   $177.50  
  Purchase #7 $64.37   12.479%   $72.4027   $72.40   $72.40   $72.40  
  7 purchase totals = $1,175.34       $1,253.5570   $1,253.55   $1,253.45   $1,253.70