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 $41.58   13.362%   $47.1359   $47.14   $47.15   $47.10  
  Purchase #2 $94.79   13.193%   $107.2956   $107.30   $107.30   $107.30  
  Purchase #3 $127.34   5.463%   $134.2966   $134.30   $134.30   $134.30  
  Purchase #4 $60.55   3.194%   $62.484   $62.48   $62.50   $62.50  
  Purchase #5 $129.94   5.433%   $136.9996   $137.00   $137.00   $137.00  
  Purchase #6 $229.64   9.321%   $251.0447   $251.04   $251.05   $251.00  
  Purchase #7 $196.41   13.194%   $222.3243   $222.32   $222.30   $222.30  
  7 purchase totals = $880.25       $961.5807   $961.58   $961.60   $961.50