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 $203.66   6.611%   $217.124   $217.12   $217.10   $217.10  
  Purchase #2 $158.62   11.512%   $176.8803   $176.88   $176.90   $176.90  
  Purchase #3 $47.56   6.592%   $50.6952   $50.70   $50.70   $50.70  
  Purchase #4 $245.93   7.568%   $264.542   $264.54   $264.55   $264.50  
  Purchase #5 $237.29   9.718%   $260.3498   $260.35   $260.35   $260.30  
  Purchase #6 $156.82   13.366%   $177.7806   $177.78   $177.80   $177.80  
  Purchase #7 $114.38   3.383%   $118.2495   $118.25   $118.25   $118.20  
  7 purchase totals = $1,164.26       $1,265.6214   $1,265.62   $1,265.65   $1,265.50