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 $41.51   12.850%   $46.844   $46.84   $46.85   $46.80  
  Purchase #2 $55.94   12.164%   $62.7445   $62.74   $62.75   $62.70  
  Purchase #3 $118.90   8.796%   $129.3584   $129.36   $129.35   $129.40  
  Purchase #4 $193.73   11.269%   $215.5614   $215.56   $215.55   $215.60  
  Purchase #5 $55.70   7.668%   $59.9711   $59.97   $59.95   $60.00  
  Purchase #6 $67.44   5.670%   $71.2638   $71.26   $71.25   $71.30  
  Purchase #7 $161.50   3.864%   $167.7404   $167.74   $167.75   $167.70  
  7 purchase totals = $694.72       $753.4836   $753.47   $753.45   $753.50