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 $226.29   13.105%   $255.9453   $255.95   $255.95   $255.90  
  Purchase #2 $200.84   4.298%   $209.4721   $209.47   $209.45   $209.50  
  Purchase #3 $96.45   11.182%   $107.235   $107.24   $107.25   $107.20  
  Purchase #4 $32.55   3.546%   $33.7042   $33.70   $33.70   $33.70  
  Purchase #5 $41.29   12.689%   $46.5293   $46.53   $46.55   $46.50  
  Purchase #6 $240.52   9.591%   $263.5883   $263.59   $263.60   $263.60  
  Purchase #7 $208.70   4.308%   $217.6908   $217.69   $217.70   $217.70  
  7 purchase totals = $1,046.64       $1,134.1650   $1,134.17   $1,134.20   $1,134.10