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 $248.84   5.648%   $262.8945   $262.89   $262.90   $262.90  
  Purchase #2 $65.72   6.519%   $70.0043   $70.00   $70.00   $70.00  
  Purchase #3 $100.99   10.399%   $111.492   $111.49   $111.50   $111.50  
  Purchase #4 $196.47   5.634%   $207.5391   $207.54   $207.55   $207.50  
  Purchase #5 $41.85   5.450%   $44.1308   $44.13   $44.15   $44.10  
  Purchase #6 $227.41   10.510%   $251.3108   $251.31   $251.30   $251.30  
  Purchase #7 $206.40   12.412%   $232.0184   $232.02   $232.00   $232.00  
  7 purchase totals = $1,087.68       $1,179.3899   $1,179.38   $1,179.40   $1,179.30