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	$11.42	12.237%	$12.8175	$12.82	$12.80	$12.80
Purchase #2	$66.96	8.869%	$72.8987	$72.90	$72.90	$72.90
Purchase #3	$73.31	13.172%	$82.9664	$82.97	$82.95	$83.00
Purchase #4	$241.70	7.521%	$259.8783	$259.88	$259.90	$259.90
Purchase #5	$167.76	10.148%	$184.7843	$184.78	$184.80	$184.80
Purchase #6	$125.43	3.362%	$129.647	$129.65	$129.65	$129.60
Purchase #7	$108.79	13.174%	$123.122	$123.12	$123.10	$123.10
7 purchase totals =	$795.37		$866.1142	$866.12	$866.10	$866.10