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 $152.68   4.536%   $159.6056   $159.61   $159.60   $159.60  
  Purchase #2 $244.61   11.797%   $273.4666   $273.47   $273.45   $273.50  
  Purchase #3 $19.66   4.496%   $20.5439   $20.54   $20.55   $20.50  
  Purchase #4 $200.26   6.315%   $212.9064   $212.91   $212.90   $212.90  
  Purchase #5 $189.42   5.842%   $200.4859   $200.49   $200.50   $200.50  
  Purchase #6 $250.61   6.664%   $267.3107   $267.31   $267.30   $267.30  
  Purchase #7 $68.42   11.658%   $76.3964   $76.40   $76.40   $76.40  
  7 purchase totals = $1,125.66       $1,210.7155   $1,210.73   $1,210.70   $1,210.70