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 $231.48   12.758%   $261.0122   $261.01   $261.00   $261.00  
  Purchase #2 $185.38   4.390%   $193.5182   $193.52   $193.50   $193.50  
  Purchase #3 $81.36   7.221%   $87.235   $87.24   $87.25   $87.20  
  Purchase #4 $234.83   6.614%   $250.3617   $250.36   $250.35   $250.40  
  Purchase #5 $96.95   8.248%   $104.9464   $104.95   $104.95   $104.90  
  Purchase #6 $59.69   11.797%   $66.7316   $66.73   $66.75   $66.70  
  Purchase #7 $206.30   8.238%   $223.295   $223.30   $223.30   $223.30  
  7 purchase totals = $1,095.99       $1,187.1001   $1,187.11   $1,187.10   $1,187.00