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	$100.59	3.192%	$103.8008	$103.80	$103.80	$103.80
Purchase #2	$152.94	11.751%	$170.912	$170.91	$170.90	$170.90
Purchase #3	$23.49	7.139%	$25.167	$25.17	$25.15	$25.20
Purchase #4	$226.38	11.103%	$251.515	$251.52	$251.50	$251.50
Purchase #5	$125.70	9.229%	$137.3009	$137.30	$137.30	$137.30
Purchase #6	$148.68	11.460%	$165.7187	$165.72	$165.70	$165.70
Purchase #7	$149.82	12.652%	$168.7752	$168.78	$168.80	$168.80
7 purchase totals =	$927.60		$1,023.1896	$1,023.20	$1,023.15	$1,023.20