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 $183.56   11.469%   $204.6125   $204.61   $204.60   $204.60  
  Purchase #2 $119.34   5.533%   $125.9431   $125.94   $125.95   $125.90  
  Purchase #3 $214.96   12.395%   $241.6043   $241.60   $241.60   $241.60  
  Purchase #4 $89.95   4.638%   $94.1219   $94.12   $94.10   $94.10  
  Purchase #5 $66.69   4.585%   $69.7477   $69.75   $69.75   $69.70  
  Purchase #6 $120.30   13.580%   $136.6367   $136.64   $136.65   $136.60  
  Purchase #7 $208.85   12.412%   $234.7725   $234.77   $234.75   $234.80  
  7 purchase totals = $1,003.65       $1,107.4387   $1,107.43   $1,107.40   $1,107.30