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	$246.83	5.187%	$259.6331	$259.63	$259.65	$259.60
Purchase #2	$170.44	11.190%	$189.5122	$189.51	$189.50	$189.50
Purchase #3	$173.43	13.523%	$196.8829	$196.88	$196.90	$196.90
Purchase #4	$35.66	8.676%	$38.7539	$38.75	$38.75	$38.80
Purchase #5	$150.50	6.281%	$159.9529	$159.95	$159.95	$160.00
Purchase #6	$89.45	6.370%	$95.148	$95.15	$95.15	$95.10
Purchase #7	$34.28	10.371%	$37.8352	$37.84	$37.85	$37.80
7 purchase totals =	$900.59		$977.7182	$977.71	$977.75	$977.70