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 $242.51   8.657%   $263.5041   $263.50   $263.50   $263.50  
  Purchase #2 $174.31   11.664%   $194.6415   $194.64   $194.65   $194.60  
  Purchase #3 $8.42   9.196%   $9.1943   $9.19   $9.20   $9.20  
  Purchase #4 $162.31   11.425%   $180.8539   $180.85   $180.85   $180.90  
  Purchase #5 $163.93   13.180%   $185.536   $185.54   $185.55   $185.50  
  Purchase #6 $10.80   12.384%   $12.1375   $12.14   $12.15   $12.10  
  Purchase #7 $182.29   12.796%   $205.6158   $205.62   $205.60   $205.60  
  7 purchase totals = $944.57       $1,051.4831   $1,051.48   $1,051.50   $1,051.40