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 $173.53   9.691%   $190.3468   $190.35   $190.35   $190.30  
  Purchase #2 $234.76   7.492%   $252.3482   $252.35   $252.35   $252.30  
  Purchase #3 $76.64   9.541%   $83.9522   $83.95   $83.95   $84.00  
  Purchase #4 $114.46   3.126%   $118.038   $118.04   $118.05   $118.00  
  Purchase #5 $177.89   10.165%   $195.9725   $195.97   $195.95   $196.00  
  Purchase #6 $60.64   9.296%   $66.2771   $66.28   $66.30   $66.30  
  Purchase #7 $14.95   4.815%   $15.6698   $15.67   $15.65   $15.70  
  7 purchase totals = $852.87       $922.6046   $922.61   $922.60   $922.60