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 $237.98   12.332%   $267.3277   $267.33   $267.35   $267.30  
  Purchase #2 $139.34   5.230%   $146.6275   $146.63   $146.65   $146.60  
  Purchase #3 $61.28   11.697%   $68.4479   $68.45   $68.45   $68.40  
  Purchase #4 $125.98   13.647%   $143.1725   $143.17   $143.15   $143.20  
  Purchase #5 $230.81   3.440%   $238.7499   $238.75   $238.75   $238.70  
  Purchase #6 $184.39   6.283%   $195.9752   $195.98   $196.00   $196.00  
  Purchase #7 $194.37   4.716%   $203.5365   $203.54   $203.55   $203.50  
  7 purchase totals = $1,174.15       $1,263.8372   $1,263.85   $1,263.90   $1,263.70