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 $148.91   11.184%   $165.5641   $165.56   $165.55   $165.60  
  Purchase #2 $239.26   9.571%   $262.1596   $262.16   $262.15   $262.20  
  Purchase #3 $60.35   3.238%   $62.3041   $62.30   $62.30   $62.30  
  Purchase #4 $162.29   11.632%   $181.1676   $181.17   $181.15   $181.20  
  Purchase #5 $195.42   3.531%   $202.3203   $202.32   $202.30   $202.30  
  Purchase #6 $30.40   8.381%   $32.9478   $32.95   $32.95   $32.90  
  Purchase #7 $135.30   5.427%   $142.6427   $142.64   $142.65   $142.60  
  7 purchase totals = $971.93       $1,049.1062   $1,049.10   $1,049.05   $1,049.10