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 $84.84   11.697%   $94.7637   $94.76   $94.75   $94.80  
  Purchase #2 $170.99   4.250%   $178.2571   $178.26   $178.25   $178.30  
  Purchase #3 $51.36   6.471%   $54.6835   $54.68   $54.70   $54.70  
  Purchase #4 $200.74   10.634%   $222.0867   $222.09   $222.10   $222.10  
  Purchase #5 $193.33   12.747%   $217.9738   $217.97   $217.95   $218.00  
  Purchase #6 $246.47   11.302%   $274.326   $274.33   $274.35   $274.30  
  Purchase #7 $7.79   3.650%   $8.0743   $8.07   $8.05   $8.10  
  7 purchase totals = $955.52       $1,050.1651   $1,050.16   $1,050.15   $1,050.30