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 $168.95   9.681%   $185.306   $185.31   $185.30   $185.30  
  Purchase #2 $240.48   9.170%   $262.532   $262.53   $262.55   $262.50  
  Purchase #3 $101.58   13.288%   $115.078   $115.08   $115.10   $115.10  
  Purchase #4 $106.50   9.489%   $116.6058   $116.61   $116.60   $116.60  
  Purchase #5 $67.46   7.711%   $72.6618   $72.66   $72.65   $72.70  
  Purchase #6 $179.58   13.448%   $203.7299   $203.73   $203.75   $203.70  
  Purchase #7 $121.45   7.235%   $130.2369   $130.24   $130.25   $130.20  
  7 purchase totals = $986.00       $1,086.1504   $1,086.16   $1,086.20   $1,086.10