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 $239.62   10.630%   $265.0916   $265.09   $265.10   $265.10  
  Purchase #2 $62.98   3.584%   $65.2372   $65.24   $65.25   $65.20  
  Purchase #3 $240.56   11.462%   $268.133   $268.13   $268.15   $268.10  
  Purchase #4 $248.39   9.483%   $271.9448   $271.94   $271.95   $271.90  
  Purchase #5 $124.38   4.257%   $129.6749   $129.67   $129.65   $129.70  
  Purchase #6 $37.29   11.351%   $41.5228   $41.52   $41.50   $41.50  
  Purchase #7 $26.43   5.344%   $27.8424   $27.84   $27.85   $27.80  
  7 purchase totals = $979.65       $1,069.4467   $1,069.43   $1,069.45   $1,069.30