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 $189.87   6.363%   $201.9514   $201.95   $201.95   $202.00  
  Purchase #2 $123.71   5.464%   $130.4695   $130.47   $130.45   $130.50  
  Purchase #3 $101.92   4.523%   $106.5298   $106.53   $106.55   $106.50  
  Purchase #4 $228.30   5.364%   $240.546   $240.55   $240.55   $240.50  
  Purchase #5 $241.68   8.235%   $261.5823   $261.58   $261.60   $261.60  
  Purchase #6 $125.27   9.774%   $137.5139   $137.51   $137.50   $137.50  
  Purchase #7 $164.55   12.272%   $184.7436   $184.74   $184.75   $184.70  
  7 purchase totals = $1,175.30       $1,263.3365   $1,263.33   $1,263.35   $1,263.30