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 $60.32   12.629%   $67.9378   $67.94   $67.95   $67.90  
  Purchase #2 $178.79   10.589%   $197.7221   $197.72   $197.70   $197.70  
  Purchase #3 $243.81   12.557%   $274.4252   $274.43   $274.45   $274.40  
  Purchase #4 $187.30   4.636%   $195.9832   $195.98   $196.00   $196.00  
  Purchase #5 $195.38   11.459%   $217.7686   $217.77   $217.75   $217.80  
  Purchase #6 $145.30   6.273%   $154.4147   $154.41   $154.40   $154.40  
  Purchase #7 $209.51   5.740%   $221.5359   $221.54   $221.55   $221.50  
  7 purchase totals = $1,220.41       $1,329.7875   $1,329.79   $1,329.80   $1,329.70