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 $62.66   10.134%   $69.01   $69.01   $69.00   $69.00  
  Purchase #2 $227.41   4.347%   $237.2955   $237.30   $237.30   $237.30  
  Purchase #3 $91.79   12.425%   $103.1949   $103.19   $103.20   $103.20  
  Purchase #4 $250.69   7.619%   $269.7901   $269.79   $269.80   $269.80  
  Purchase #5 $55.62   3.664%   $57.6579   $57.66   $57.65   $57.70  
  Purchase #6 $33.67   13.693%   $38.2804   $38.28   $38.30   $38.30  
  Purchase #7 $173.41   12.557%   $195.1851   $195.19   $195.20   $195.20  
  7 purchase totals = $895.25       $970.4139   $970.42   $970.45   $970.50