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 $94.81   6.798%   $101.2552   $101.26   $101.25   $101.30  
  Purchase #2 $236.42   3.370%   $244.3874   $244.39   $244.40   $244.40  
  Purchase #3 $232.56   8.837%   $253.1113   $253.11   $253.10   $253.10  
  Purchase #4 $220.26   12.532%   $247.863   $247.86   $247.85   $247.90  
  Purchase #5 $160.40   10.288%   $176.902   $176.90   $176.90   $176.90  
  Purchase #6 $209.28   6.321%   $222.5086   $222.51   $222.50   $222.50  
  Purchase #7 $123.39   6.378%   $131.2598   $131.26   $131.25   $131.30  
  7 purchase totals = $1,277.12       $1,377.2873   $1,377.29   $1,377.25   $1,377.40