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 $202.48   3.468%   $209.502   $209.50   $209.50   $209.50  
  Purchase #2 $109.64   3.312%   $113.2713   $113.27   $113.25   $113.30  
  Purchase #3 $115.68   4.241%   $120.586   $120.59   $120.60   $120.60  
  Purchase #4 $151.46   10.726%   $167.7056   $167.71   $167.70   $167.70  
  Purchase #5 $217.48   13.659%   $247.1856   $247.19   $247.20   $247.20  
  Purchase #6 $24.91   3.145%   $25.6934   $25.69   $25.70   $25.70  
  Purchase #7 $156.76   4.428%   $163.7013   $163.70   $163.70   $163.70  
  7 purchase totals = $978.41       $1,047.6452   $1,047.65   $1,047.65   $1,047.70