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	$132.89	4.716%	$139.1571	$139.16	$139.15	$139.20
Purchase #2	$21.98	13.276%	$24.8981	$24.90	$24.90	$24.90
Purchase #3	$82.25	10.230%	$90.6642	$90.66	$90.65	$90.70
Purchase #4	$219.37	7.312%	$235.4103	$235.41	$235.40	$235.40
Purchase #5	$215.47	4.788%	$225.7867	$225.79	$225.80	$225.80
Purchase #6	$29.57	13.793%	$33.6486	$33.65	$33.65	$33.60
Purchase #7	$38.80	7.674%	$41.7775	$41.78	$41.80	$41.80
7 purchase totals =	$740.33		$791.3425	$791.35	$791.35	$791.40