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	$209.34	6.532%	$223.0141	$223.01	$223.00	$223.00
Purchase #2	$223.36	3.654%	$231.5216	$231.52	$231.50	$231.50
Purchase #3	$129.61	8.195%	$140.2315	$140.23	$140.25	$140.20
Purchase #4	$117.37	8.833%	$127.7373	$127.74	$127.75	$127.70
Purchase #5	$125.46	7.516%	$134.8896	$134.89	$134.90	$134.90
Purchase #6	$54.78	9.111%	$59.771	$59.77	$59.75	$59.80
Purchase #7	$49.69	12.158%	$55.7313	$55.73	$55.75	$55.70
7 purchase totals =	$909.61		$972.8964	$972.89	$972.90	$972.80