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 $237.49   4.717%   $248.6924   $248.69   $248.70   $248.70  
  Purchase #2 $211.71   4.565%   $221.3746   $221.37   $221.35   $221.40  
  Purchase #3 $162.60   7.636%   $175.0161   $175.02   $175.00   $175.00  
  Purchase #4 $199.73   6.488%   $212.6885   $212.69   $212.70   $212.70  
  Purchase #5 $175.40   3.421%   $181.4004   $181.40   $181.40   $181.40  
  Purchase #6 $237.56   11.669%   $265.2809   $265.28   $265.30   $265.30  
  Purchase #7 $51.90   5.303%   $54.6523   $54.65   $54.65   $54.70  
  7 purchase totals = $1,276.39       $1,359.1052   $1,359.10   $1,359.10   $1,359.20