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 $165.48   12.322%   $185.8704   $185.87   $185.85   $185.90  
  Purchase #2 $198.99   9.854%   $218.5985   $218.60   $218.60   $218.60  
  Purchase #3 $229.99   9.666%   $252.2208   $252.22   $252.20   $252.20  
  Purchase #4 $63.57   3.294%   $65.664   $65.66   $65.65   $65.70  
  Purchase #5 $94.73   10.637%   $104.8064   $104.81   $104.80   $104.80  
  Purchase #6 $61.57   10.187%   $67.8421   $67.84   $67.85   $67.80  
  Purchase #7 $199.44   3.593%   $206.6059   $206.61   $206.60   $206.60  
  7 purchase totals = $1,013.77       $1,101.6081   $1,101.61   $1,101.55   $1,101.60