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 $240.27   8.760%   $261.3177   $261.32   $261.30   $261.30  
  Purchase #2 $243.93   8.535%   $264.7494   $264.75   $264.75   $264.70  
  Purchase #3 $77.91   6.208%   $82.7467   $82.75   $82.75   $82.70  
  Purchase #4 $55.63   13.761%   $63.2852   $63.29   $63.30   $63.30  
  Purchase #5 $65.32   9.223%   $71.3445   $71.34   $71.35   $71.30  
  Purchase #6 $248.44   12.336%   $279.0876   $279.09   $279.10   $279.10  
  Purchase #7 $157.95   7.641%   $170.019   $170.02   $170.00   $170.00  
  7 purchase totals = $1,089.45       $1,192.5501   $1,192.56   $1,192.55   $1,192.40