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 $60.81   13.190%   $68.8308   $68.83   $68.85   $68.80  
  Purchase #2 $191.59   10.617%   $211.9311   $211.93   $211.95   $211.90  
  Purchase #3 $78.39   9.188%   $85.5925   $85.59   $85.60   $85.60  
  Purchase #4 $175.68   9.557%   $192.4697   $192.47   $192.45   $192.50  
  Purchase #5 $217.71   3.227%   $224.7355   $224.74   $224.75   $224.70  
  Purchase #6 $133.45   9.546%   $146.1891   $146.19   $146.20   $146.20  
  Purchase #7 $175.47   13.461%   $199.09   $199.09   $199.10   $199.10  
  7 purchase totals = $1,033.10       $1,128.8387   $1,128.84   $1,128.90   $1,128.80