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	$245.90	13.332%	$278.6834	$278.68	$278.70	$278.70
Purchase #2	$51.88	13.165%	$58.71	$58.71	$58.70	$58.70
Purchase #3	$88.89	3.170%	$91.7078	$91.71	$91.70	$91.70
Purchase #4	$100.58	9.755%	$110.3916	$110.39	$110.40	$110.40
Purchase #5	$196.48	13.235%	$222.4841	$222.48	$222.50	$222.50
Purchase #6	$164.88	3.258%	$170.2518	$170.25	$170.25	$170.30
Purchase #7	$67.43	5.221%	$70.9505	$70.95	$70.95	$71.00
7 purchase totals =	$916.04		$1,003.1792	$1,003.17	$1,003.20	$1,003.30