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	$171.25	9.727%	$187.9075	$187.91	$187.90	$187.90
Purchase #2	$34.79	11.265%	$38.7091	$38.71	$38.70	$38.70
Purchase #3	$88.68	12.463%	$99.7322	$99.73	$99.75	$99.70
Purchase #4	$47.31	13.658%	$53.7716	$53.77	$53.75	$53.80
Purchase #5	$150.75	13.605%	$171.2595	$171.26	$171.25	$171.30
Purchase #6	$223.75	4.360%	$233.5055	$233.51	$233.50	$233.50
Purchase #7	$67.90	9.764%	$74.5298	$74.53	$74.55	$74.50
7 purchase totals =	$784.43		$859.4152	$859.42	$859.40	$859.40