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 $241.48   11.110%   $268.3084   $268.31   $268.30   $268.30  
  Purchase #2 $196.91   6.816%   $210.3314   $210.33   $210.35   $210.30  
  Purchase #3 $140.52   12.800%   $158.5066   $158.51   $158.50   $158.50  
  Purchase #4 $72.58   7.202%   $77.8072   $77.81   $77.80   $77.80  
  Purchase #5 $80.58   9.552%   $88.277   $88.28   $88.30   $88.30  
  Purchase #6 $185.69   9.797%   $203.882   $203.88   $203.90   $203.90  
  Purchase #7 $49.47   4.772%   $51.8307   $51.83   $51.85   $51.80  
  7 purchase totals = $967.23       $1,058.9433   $1,058.95   $1,059.00   $1,058.90