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 $89.32   6.577%   $95.1946   $95.19   $95.20   $95.20  
  Purchase #2 $111.76   10.302%   $123.2735   $123.27   $123.25   $123.30  
  Purchase #3 $54.54   7.583%   $58.6758   $58.68   $58.70   $58.70  
  Purchase #4 $60.72   8.643%   $65.968   $65.97   $65.95   $66.00  
  Purchase #5 $177.79   5.412%   $187.412   $187.41   $187.40   $187.40  
  Purchase #6 $205.63   9.496%   $225.1566   $225.16   $225.15   $225.20  
  Purchase #7 $145.44   8.715%   $158.1151   $158.12   $158.10   $158.10  
  7 purchase totals = $845.20       $913.7956   $913.80   $913.75   $913.90