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 $239.98   8.755%   $260.9902   $260.99   $261.00   $261.00  
  Purchase #2 $110.48   8.241%   $119.5847   $119.58   $119.60   $119.60  
  Purchase #3 $154.82   13.360%   $175.504   $175.50   $175.50   $175.50  
  Purchase #4 $167.37   5.274%   $176.1971   $176.20   $176.20   $176.20  
  Purchase #5 $58.67   13.317%   $66.4831   $66.48   $66.50   $66.50  
  Purchase #6 $70.46   5.231%   $74.1458   $74.15   $74.15   $74.10  
  Purchase #7 $186.89   13.117%   $211.4044   $211.40   $211.40   $211.40  
  7 purchase totals = $988.67       $1,084.3093   $1,084.30   $1,084.35   $1,084.30