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 $211.66   7.450%   $227.4287   $227.43   $227.45   $227.40  
  Purchase #2 $189.86   6.525%   $202.2484   $202.25   $202.25   $202.20  
  Purchase #3 $24.70   5.134%   $25.9681   $25.97   $25.95   $26.00  
  Purchase #4 $83.86   12.861%   $94.6452   $94.65   $94.65   $94.60  
  Purchase #5 $248.40   5.251%   $261.4435   $261.44   $261.45   $261.40  
  Purchase #6 $226.74   12.462%   $254.9963   $255.00   $255.00   $255.00  
  Purchase #7 $137.74   9.421%   $150.7165   $150.72   $150.70   $150.70  
  7 purchase totals = $1,122.96       $1,217.4467   $1,217.46   $1,217.45   $1,217.30