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 $162.91   8.228%   $176.3142   $176.31   $176.30   $176.30  
  Purchase #2 $212.99   5.445%   $224.5873   $224.59   $224.60   $224.60  
  Purchase #3 $117.32   3.159%   $121.0261   $121.03   $121.05   $121.00  
  Purchase #4 $78.98   12.598%   $88.9299   $88.93   $88.95   $88.90  
  Purchase #5 $205.55   5.277%   $216.3969   $216.40   $216.40   $216.40  
  Purchase #6 $30.33   13.241%   $34.346   $34.35   $34.35   $34.30  
  Purchase #7 $114.44   4.858%   $119.9995   $120.00   $120.00   $120.00  
  7 purchase totals = $922.52       $981.5999   $981.61   $981.65   $981.50