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 $201.26   6.475%   $214.2916   $214.29   $214.30   $214.30  
  Purchase #2 $146.41   7.216%   $156.9749   $156.97   $156.95   $157.00  
  Purchase #3 $14.75   12.457%   $16.5874   $16.59   $16.60   $16.60  
  Purchase #4 $125.52   9.518%   $137.467   $137.47   $137.45   $137.50  
  Purchase #5 $120.85   8.116%   $130.6582   $130.66   $130.65   $130.70  
  Purchase #6 $80.60   3.539%   $83.4524   $83.45   $83.45   $83.50  
  Purchase #7 $151.84   7.325%   $162.9623   $162.96   $162.95   $163.00  
  7 purchase totals = $841.23       $902.3938   $902.39   $902.35   $902.60