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 $24.81   3.571%   $25.696   $25.70   $25.70   $25.70  
  Purchase #2 $144.41   4.331%   $150.6644   $150.66   $150.65   $150.70  
  Purchase #3 $16.35   3.116%   $16.8595   $16.86   $16.85   $16.90  
  Purchase #4 $126.57   12.844%   $142.8267   $142.83   $142.85   $142.80  
  Purchase #5 $162.71   6.103%   $172.6402   $172.64   $172.65   $172.60  
  Purchase #6 $39.33   12.185%   $44.1224   $44.12   $44.10   $44.10  
  Purchase #7 $248.99   5.356%   $262.3259   $262.33   $262.35   $262.30  
  7 purchase totals = $763.17       $815.1351   $815.14   $815.15   $815.10