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 $237.33   13.102%   $268.425   $268.43   $268.45   $268.40  
  Purchase #2 $15.49   8.256%   $16.7689   $16.77   $16.75   $16.80  
  Purchase #3 $222.36   5.170%   $233.856   $233.86   $233.85   $233.90  
  Purchase #4 $36.27   5.158%   $38.1408   $38.14   $38.15   $38.10  
  Purchase #5 $247.56   5.124%   $260.245   $260.25   $260.25   $260.20  
  Purchase #6 $56.32   4.867%   $59.0611   $59.06   $59.05   $59.10  
  Purchase #7 $150.74   10.784%   $166.9958   $167.00   $167.00   $167.00  
  7 purchase totals = $966.07       $1,043.4926   $1,043.51   $1,043.50   $1,043.50