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 $234.57   10.825%   $259.9622   $259.96   $259.95   $260.00  
  Purchase #2 $88.57   3.587%   $91.747   $91.75   $91.75   $91.70  
  Purchase #3 $193.93   11.512%   $216.2552   $216.26   $216.25   $216.30  
  Purchase #4 $105.86   7.219%   $113.502   $113.50   $113.50   $113.50  
  Purchase #5 $177.27   7.344%   $190.2887   $190.29   $190.30   $190.30  
  Purchase #6 $68.31   13.518%   $77.5441   $77.54   $77.55   $77.50  
  Purchase #7 $195.67   11.669%   $218.5027   $218.50   $218.50   $218.50  
  7 purchase totals = $1,064.18       $1,167.8019   $1,167.80   $1,167.80   $1,167.80