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	$216.38	3.188%	$223.2782	$223.28	$223.30	$223.30
Purchase #2	$20.56	10.803%	$22.7811	$22.78	$22.80	$22.80
Purchase #3	$123.71	6.290%	$131.4914	$131.49	$131.50	$131.50
Purchase #4	$110.85	3.261%	$114.4648	$114.46	$114.45	$114.50
Purchase #5	$75.45	8.860%	$82.1349	$82.13	$82.15	$82.10
Purchase #6	$27.82	11.359%	$30.9801	$30.98	$31.00	$31.00
Purchase #7	$146.89	3.701%	$152.3264	$152.33	$152.35	$152.30
7 purchase totals =	$721.66		$757.4569	$757.45	$757.55	$757.50