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 $107.66   11.212%   $119.7308   $119.73   $119.75   $119.70  
  Purchase #2 $225.71   9.250%   $246.5882   $246.59   $246.60   $246.60  
  Purchase #3 $212.25   9.136%   $231.6412   $231.64   $231.65   $231.60  
  Purchase #4 $100.85   6.755%   $107.6624   $107.66   $107.65   $107.70  
  Purchase #5 $21.26   7.758%   $22.9094   $22.91   $22.90   $22.90  
  Purchase #6 $214.65   6.594%   $228.804   $228.80   $228.80   $228.80  
  Purchase #7 $45.34   11.247%   $50.4394   $50.44   $50.45   $50.40  
  7 purchase totals = $927.72       $1,007.7754   $1,007.77   $1,007.80   $1,007.70