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 $58.99   6.189%   $62.6409   $62.64   $62.65   $62.60  
  Purchase #2 $149.31   3.173%   $154.0476   $154.05   $154.05   $154.00  
  Purchase #3 $114.58   11.288%   $127.5138   $127.51   $127.50   $127.50  
  Purchase #4 $237.63   12.863%   $268.1963   $268.20   $268.20   $268.20  
  Purchase #5 $14.43   7.648%   $15.5336   $15.53   $15.55   $15.50  
  Purchase #6 $123.35   8.864%   $134.2837   $134.28   $134.30   $134.30  
  Purchase #7 $154.36   7.444%   $165.8506   $165.85   $165.85   $165.90  
  7 purchase totals = $852.65       $928.0665   $928.06   $928.10   $928.00