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 $165.38   11.702%   $184.7328   $184.73   $184.75   $184.70  
  Purchase #2 $243.63   13.520%   $276.5688   $276.57   $276.55   $276.60  
  Purchase #3 $144.91   4.450%   $151.3585   $151.36   $151.35   $151.40  
  Purchase #4 $200.53   7.114%   $214.7957   $214.80   $214.80   $214.80  
  Purchase #5 $226.92   11.783%   $253.658   $253.66   $253.65   $253.70  
  Purchase #6 $61.89   11.802%   $69.1943   $69.19   $69.20   $69.20  
  Purchase #7 $108.68   9.306%   $118.7938   $118.79   $118.80   $118.80  
  7 purchase totals = $1,151.94       $1,269.1019   $1,269.10   $1,269.10   $1,269.20