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 $116.38   7.231%   $124.7954   $124.80   $124.80   $124.80  
  Purchase #2 $139.91   6.456%   $148.9426   $148.94   $148.95   $148.90  
  Purchase #3 $236.97   12.105%   $265.6552   $265.66   $265.65   $265.70  
  Purchase #4 $122.84   5.404%   $129.4783   $129.48   $129.50   $129.50  
  Purchase #5 $113.34   8.126%   $122.55   $122.55   $122.55   $122.60  
  Purchase #6 $127.32   6.848%   $136.0389   $136.04   $136.05   $136.00  
  Purchase #7 $163.92   7.686%   $176.5189   $176.52   $176.50   $176.50  
  7 purchase totals = $1,020.68       $1,103.9793   $1,103.99   $1,104.00   $1,104.00