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	$12.95	3.591%	$13.415	$13.42	$13.40	$13.40
Purchase #2	$63.33	4.707%	$66.3109	$66.31	$66.30	$66.30
Purchase #3	$198.50	12.458%	$223.2291	$223.23	$223.25	$223.20
Purchase #4	$82.54	13.530%	$93.7077	$93.71	$93.70	$93.70
Purchase #5	$19.75	7.777%	$21.286	$21.29	$21.30	$21.30
Purchase #6	$247.28	13.588%	$280.8804	$280.88	$280.90	$280.90
Purchase #7	$39.85	6.635%	$42.494	$42.49	$42.50	$42.50
7 purchase totals =	$664.20		$741.3231	$741.33	$741.35	$741.30