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 $50.54   6.107%   $53.6265   $53.63   $53.65   $53.60  
  Purchase #2 $71.58   6.836%   $76.4732   $76.47   $76.45   $76.50  
  Purchase #3 $179.61   8.569%   $195.0008   $195.00   $195.00   $195.00  
  Purchase #4 $217.31   3.605%   $225.144   $225.14   $225.15   $225.10  
  Purchase #5 $202.25   7.664%   $217.7504   $217.75   $217.75   $217.80  
  Purchase #6 $184.83   13.691%   $210.1351   $210.14   $210.15   $210.10  
  Purchase #7 $65.30   12.568%   $73.5069   $73.51   $73.50   $73.50  
  7 purchase totals = $971.42       $1,051.6369   $1,051.64   $1,051.65   $1,051.60