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	$33.45	5.433%	$35.2673	$35.27	$35.25	$35.30
Purchase #2	$25.89	10.356%	$28.5712	$28.57	$28.55	$28.60
Purchase #3	$33.80	4.546%	$35.3365	$35.34	$35.35	$35.30
Purchase #4	$37.25	12.791%	$42.0146	$42.01	$42.00	$42.00
Purchase #5	$170.52	5.659%	$180.1697	$180.17	$180.15	$180.20
Purchase #6	$62.88	3.582%	$65.1324	$65.13	$65.15	$65.10
Purchase #7	$131.65	13.861%	$149.898	$149.90	$149.90	$149.90
7 purchase totals =	$495.44		$536.3897	$536.39	$536.35	$536.40