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 $246.95   11.725%   $275.9049   $275.90   $275.90   $275.90  
  Purchase #2 $209.65   12.543%   $235.9464   $235.95   $235.95   $235.90  
  Purchase #3 $107.91   5.363%   $113.6972   $113.70   $113.70   $113.70  
  Purchase #4 $212.48   7.564%   $228.552   $228.55   $228.55   $228.60  
  Purchase #5 $194.83   8.146%   $210.7009   $210.70   $210.70   $210.70  
  Purchase #6 $55.79   10.193%   $61.4767   $61.48   $61.50   $61.50  
  Purchase #7 $236.39   10.534%   $261.2913   $261.29   $261.30   $261.30  
  7 purchase totals = $1,264.00       $1,387.5694   $1,387.57   $1,387.60   $1,387.60