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 $248.88   11.396%   $277.2424   $277.24   $277.25   $277.20  
  Purchase #2 $89.28   6.338%   $94.9386   $94.94   $94.95   $94.90  
  Purchase #3 $119.85   10.821%   $132.819   $132.82   $132.80   $132.80  
  Purchase #4 $239.43   10.174%   $263.7896   $263.79   $263.80   $263.80  
  Purchase #5 $11.37   6.753%   $12.1378   $12.14   $12.15   $12.10  
  Purchase #6 $86.89   11.379%   $96.7772   $96.78   $96.80   $96.80  
  Purchase #7 $152.53   12.725%   $171.9394   $171.94   $171.95   $171.90  
  7 purchase totals = $948.23       $1,049.6440   $1,049.65   $1,049.70   $1,049.50