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 $184.42   6.268%   $195.9794   $195.98   $196.00   $196.00  
  Purchase #2 $37.86   11.423%   $42.1847   $42.18   $42.20   $42.20  
  Purchase #3 $53.92   3.325%   $55.7128   $55.71   $55.70   $55.70  
  Purchase #4 $115.26   6.426%   $122.6666   $122.67   $122.65   $122.70  
  Purchase #5 $132.92   3.424%   $137.4712   $137.47   $137.45   $137.50  
  Purchase #6 $45.54   5.113%   $47.8685   $47.87   $47.85   $47.90  
  Purchase #7 $124.93   10.732%   $138.3375   $138.34   $138.35   $138.30  
  7 purchase totals = $694.85       $740.2207   $740.22   $740.20   $740.30