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 $213.59   4.402%   $222.9922   $222.99   $223.00   $223.00  
  Purchase #2 $30.66   8.592%   $33.2943   $33.29   $33.30   $33.30  
  Purchase #3 $159.53   5.656%   $168.553   $168.55   $168.55   $168.60  
  Purchase #4 $124.29   13.177%   $140.6677   $140.67   $140.65   $140.70  
  Purchase #5 $162.49   4.798%   $170.2863   $170.29   $170.30   $170.30  
  Purchase #6 $204.49   6.598%   $217.9823   $217.98   $218.00   $218.00  
  Purchase #7 $44.74   8.649%   $48.6096   $48.61   $48.60   $48.60  
  7 purchase totals = $939.79       $1,002.3854   $1,002.38   $1,002.40   $1,002.50