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 $193.33   6.145%   $205.2101   $205.21   $205.20   $205.20  
  Purchase #2 $250.55   7.165%   $268.5019   $268.50   $268.50   $268.50  
  Purchase #3 $124.69   6.199%   $132.4195   $132.42   $132.40   $132.40  
  Purchase #4 $241.95   11.319%   $269.3363   $269.34   $269.35   $269.30  
  Purchase #5 $81.35   11.335%   $90.571   $90.57   $90.55   $90.60  
  Purchase #6 $81.27   3.591%   $84.1884   $84.19   $84.20   $84.20  
  Purchase #7 $156.25   12.235%   $175.3672   $175.37   $175.35   $175.40  
  7 purchase totals = $1,129.39       $1,225.5944   $1,225.60   $1,225.55   $1,225.60