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 $222.76   6.701%   $237.6871   $237.69   $237.70   $237.70  
  Purchase #2 $194.34   13.458%   $220.4943   $220.49   $220.50   $220.50  
  Purchase #3 $54.63   7.820%   $58.9021   $58.90   $58.90   $58.90  
  Purchase #4 $131.41   11.633%   $146.6969   $146.70   $146.70   $146.70  
  Purchase #5 $114.31   13.616%   $129.8744   $129.87   $129.85   $129.90  
  Purchase #6 $25.32   5.170%   $26.629   $26.63   $26.65   $26.60  
  Purchase #7 $180.30   4.257%   $187.9754   $187.98   $188.00   $188.00  
  7 purchase totals = $923.07       $1,008.2592   $1,008.26   $1,008.30   $1,008.30