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 $184.92   11.717%   $206.5871   $206.59   $206.60   $206.60  
  Purchase #2 $92.65   5.707%   $97.9375   $97.94   $97.95   $97.90  
  Purchase #3 $95.58   5.617%   $100.9487   $100.95   $100.95   $100.90  
  Purchase #4 $11.36   8.433%   $12.318   $12.32   $12.30   $12.30  
  Purchase #5 $138.92   10.758%   $153.865   $153.87   $153.85   $153.90  
  Purchase #6 $187.27   13.597%   $212.7331   $212.73   $212.75   $212.70  
  Purchase #7 $244.68   11.258%   $272.2261   $272.23   $272.25   $272.20  
  7 purchase totals = $955.38       $1,056.6155   $1,056.63   $1,056.65   $1,056.50