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 $59.38   3.599%   $61.5171   $61.52   $61.50   $61.50  
  Purchase #2 $190.87   10.158%   $210.2586   $210.26   $210.25   $210.30  
  Purchase #3 $12.26   9.783%   $13.4594   $13.46   $13.45   $13.50  
  Purchase #4 $247.40   4.301%   $258.0407   $258.04   $258.05   $258.00  
  Purchase #5 $169.40   11.827%   $189.4349   $189.43   $189.45   $189.40  
  Purchase #6 $69.81   8.272%   $75.5847   $75.58   $75.60   $75.60  
  Purchase #7 $229.93   5.380%   $242.3002   $242.30   $242.30   $242.30  
  7 purchase totals = $979.05       $1,050.5956   $1,050.59   $1,050.60   $1,050.60