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 $241.27   8.777%   $262.4463   $262.45   $262.45   $262.40  
  Purchase #2 $216.58   7.178%   $232.1261   $232.13   $232.15   $232.10  
  Purchase #3 $239.26   10.224%   $263.7219   $263.72   $263.70   $263.70  
  Purchase #4 $130.26   6.215%   $138.3557   $138.36   $138.35   $138.40  
  Purchase #5 $116.71   13.556%   $132.5312   $132.53   $132.55   $132.50  
  Purchase #6 $245.99   7.853%   $265.3076   $265.31   $265.30   $265.30  
  Purchase #7 $228.55   11.394%   $254.591   $254.59   $254.60   $254.60  
  7 purchase totals = $1,418.62       $1,549.0798   $1,549.09   $1,549.10   $1,549.00