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 $47.83   6.227%   $50.8084   $50.81   $50.80   $50.80  
  Purchase #2 $144.67   3.602%   $149.881   $149.88   $149.90   $149.90  
  Purchase #3 $172.99   5.536%   $182.5667   $182.57   $182.55   $182.60  
  Purchase #4 $230.56   12.550%   $259.4953   $259.50   $259.50   $259.50  
  Purchase #5 $114.29   10.204%   $125.9522   $125.95   $125.95   $126.00  
  Purchase #6 $177.75   10.528%   $196.4635   $196.46   $196.45   $196.50  
  Purchase #7 $83.42   3.251%   $86.132   $86.13   $86.15   $86.10  
  7 purchase totals = $971.51       $1,051.2991   $1,051.30   $1,051.30   $1,051.40