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	$171.46	7.613%	$184.5132	$184.51	$184.50	$184.50
Purchase #2	$179.46	8.333%	$194.4144	$194.41	$194.40	$194.40
Purchase #3	$72.55	10.690%	$80.3056	$80.31	$80.30	$80.30
Purchase #4	$139.65	6.655%	$148.9437	$148.94	$148.95	$148.90
Purchase #5	$56.75	7.770%	$61.1595	$61.16	$61.15	$61.20
Purchase #6	$246.37	13.188%	$278.8613	$278.86	$278.85	$278.90
Purchase #7	$165.85	10.685%	$183.5711	$183.57	$183.55	$183.60
7 purchase totals =	$1,032.09		$1,131.7688	$1,131.76	$1,131.70	$1,131.80