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 $104.25   13.485%   $118.3081   $118.31   $118.30   $118.30  
  Purchase #2 $223.74   5.771%   $236.652   $236.65   $236.65   $236.70  
  Purchase #3 $55.66   11.291%   $61.9446   $61.94   $61.95   $61.90  
  Purchase #4 $56.44   7.873%   $60.8835   $60.88   $60.90   $60.90  
  Purchase #5 $68.91   10.403%   $76.0787   $76.08   $76.10   $76.10  
  Purchase #6 $120.72   6.554%   $128.632   $128.63   $128.65   $128.60  
  Purchase #7 $38.35   10.301%   $42.3004   $42.30   $42.30   $42.30  
  7 purchase totals = $668.07       $724.7993   $724.79   $724.85   $724.80