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 $89.62   3.360%   $92.6312   $92.63   $92.65   $92.60  
  Purchase #2 $200.72   11.431%   $223.6643   $223.66   $223.65   $223.70  
  Purchase #3 $249.68   6.536%   $265.9991   $266.00   $266.00   $266.00  
  Purchase #4 $214.62   7.428%   $230.562   $230.56   $230.55   $230.60  
  Purchase #5 $119.36   5.554%   $125.9893   $125.99   $126.00   $126.00  
  Purchase #6 $41.36   8.511%   $44.8801   $44.88   $44.90   $44.90  
  Purchase #7 $139.65   9.768%   $153.291   $153.29   $153.30   $153.30  
  7 purchase totals = $1,055.01       $1,137.0170   $1,137.01   $1,137.05   $1,137.10