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 $180.27   12.776%   $203.3013   $203.30   $203.30   $203.30  
  Purchase #2 $169.33   4.160%   $176.3741   $176.37   $176.35   $176.40  
  Purchase #3 $69.97   10.826%   $77.545   $77.55   $77.55   $77.50  
  Purchase #4 $118.89   8.744%   $129.2857   $129.29   $129.30   $129.30  
  Purchase #5 $184.31   12.219%   $206.8308   $206.83   $206.85   $206.80  
  Purchase #6 $211.25   11.836%   $236.2536   $236.25   $236.25   $236.30  
  Purchase #7 $234.51   7.673%   $252.504   $252.50   $252.50   $252.50  
  7 purchase totals = $1,168.53       $1,282.0945   $1,282.09   $1,282.10   $1,282.10