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 $184.62   11.314%   $205.5079   $205.51   $205.50   $205.50  
  Purchase #2 $64.62   3.114%   $66.6323   $66.63   $66.65   $66.60  
  Purchase #3 $44.37   5.122%   $46.6426   $46.64   $46.65   $46.60  
  Purchase #4 $207.90   10.108%   $228.9145   $228.91   $228.90   $228.90  
  Purchase #5 $81.59   3.567%   $84.5003   $84.50   $84.50   $84.50  
  Purchase #6 $197.53   8.611%   $214.5393   $214.54   $214.55   $214.50  
  Purchase #7 $206.49   9.749%   $226.6207   $226.62   $226.60   $226.60  
  7 purchase totals = $987.12       $1,073.3576   $1,073.35   $1,073.35   $1,073.20