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 $106.52   11.124%   $118.3693   $118.37   $118.35   $118.40  
  Purchase #2 $101.94   8.521%   $110.6263   $110.63   $110.65   $110.60  
  Purchase #3 $8.76   12.187%   $9.8276   $9.83   $9.85   $9.80  
  Purchase #4 $121.62   6.109%   $129.0498   $129.05   $129.05   $129.00  
  Purchase #5 $167.85   10.640%   $185.7092   $185.71   $185.70   $185.70  
  Purchase #6 $58.50   13.589%   $66.4496   $66.45   $66.45   $66.40  
  Purchase #7 $101.80   5.680%   $107.5822   $107.58   $107.60   $107.60  
  7 purchase totals = $666.99       $727.6140   $727.62   $727.65   $727.50