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 $186.97   10.155%   $205.9568   $205.96   $205.95   $206.00  
  Purchase #2 $127.39   4.706%   $133.385   $133.39   $133.40   $133.40  
  Purchase #3 $97.92   3.757%   $101.5989   $101.60   $101.60   $101.60  
  Purchase #4 $162.54   7.121%   $174.1145   $174.11   $174.10   $174.10  
  Purchase #5 $149.60   10.742%   $165.67   $165.67   $165.65   $165.70  
  Purchase #6 $240.80   11.519%   $268.5378   $268.54   $268.55   $268.50  
  Purchase #7 $209.64   12.441%   $235.7213   $235.72   $235.70   $235.70  
  7 purchase totals = $1,174.86       $1,284.9843   $1,284.99   $1,284.95   $1,285.00