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 $60.84   9.702%   $66.7427   $66.74   $66.75   $66.70  
  Purchase #2 $123.96   6.866%   $132.4711   $132.47   $132.45   $132.50  
  Purchase #3 $75.67   11.781%   $84.5847   $84.58   $84.60   $84.60  
  Purchase #4 $233.31   5.417%   $245.9484   $245.95   $245.95   $245.90  
  Purchase #5 $168.61   13.376%   $191.1633   $191.16   $191.15   $191.20  
  Purchase #6 $215.63   5.133%   $226.6983   $226.70   $226.70   $226.70  
  Purchase #7 $31.72   6.389%   $33.7466   $33.75   $33.75   $33.70  
  7 purchase totals = $909.74       $981.3551   $981.35   $981.35   $981.30