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 $194.57   6.177%   $206.5886   $206.59   $206.60   $206.60  
  Purchase #2 $98.80   11.562%   $110.2233   $110.22   $110.20   $110.20  
  Purchase #3 $78.73   5.315%   $82.9145   $82.91   $82.90   $82.90  
  Purchase #4 $159.67   9.771%   $175.2714   $175.27   $175.25   $175.30  
  Purchase #5 $163.97   4.842%   $171.9094   $171.91   $171.90   $171.90  
  Purchase #6 $136.91   3.140%   $141.209   $141.21   $141.20   $141.20  
  Purchase #7 $84.73   12.758%   $95.5399   $95.54   $95.55   $95.50  
  7 purchase totals = $917.38       $983.6561   $983.65   $983.60   $983.60