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 $204.88   3.640%   $212.3376   $212.34   $212.35   $212.30  
  Purchase #2 $95.64   5.281%   $100.6907   $100.69   $100.70   $100.70  
  Purchase #3 $233.44   3.505%   $241.6221   $241.62   $241.60   $241.60  
  Purchase #4 $232.78   12.533%   $261.9543   $261.95   $261.95   $262.00  
  Purchase #5 $150.90   8.801%   $164.1807   $164.18   $164.20   $164.20  
  Purchase #6 $106.37   6.416%   $113.1947   $113.19   $113.20   $113.20  
  Purchase #7 $140.99   5.851%   $149.2393   $149.24   $149.25   $149.20  
  7 purchase totals = $1,165.00       $1,243.2194   $1,243.21   $1,243.25   $1,243.20