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 $246.27   3.121%   $253.9561   $253.96   $253.95   $254.00  
  Purchase #2 $206.86   7.643%   $222.6703   $222.67   $222.65   $222.70  
  Purchase #3 $248.80   4.236%   $259.3392   $259.34   $259.35   $259.30  
  Purchase #4 $66.98   5.723%   $70.8133   $70.81   $70.80   $70.80  
  Purchase #5 $167.63   8.263%   $181.4813   $181.48   $181.50   $181.50  
  Purchase #6 $208.94   5.732%   $220.9164   $220.92   $220.90   $220.90  
  Purchase #7 $211.45   12.381%   $237.6296   $237.63   $237.65   $237.60  
  7 purchase totals = $1,356.93       $1,446.8062   $1,446.81   $1,446.80   $1,446.80