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 $85.33   9.729%   $93.6318   $93.63   $93.65   $93.60  
  Purchase #2 $207.85   7.271%   $222.9628   $222.96   $222.95   $223.00  
  Purchase #3 $97.26   9.571%   $106.5688   $106.57   $106.55   $106.60  
  Purchase #4 $26.49   12.218%   $29.7265   $29.73   $29.75   $29.70  
  Purchase #5 $113.96   9.210%   $124.4557   $124.46   $124.45   $124.50  
  Purchase #6 $96.71   3.317%   $99.9179   $99.92   $99.90   $99.90  
  Purchase #7 $154.61   9.711%   $169.6242   $169.62   $169.60   $169.60  
  7 purchase totals = $782.21       $846.8877   $846.89   $846.85   $846.90