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	$132.58	3.140%	$136.743	$136.74	$136.75	$136.70
Purchase #2	$131.96	11.524%	$147.1671	$147.17	$147.15	$147.20
Purchase #3	$209.43	11.535%	$233.5878	$233.59	$233.60	$233.60
Purchase #4	$242.69	5.767%	$256.6859	$256.69	$256.70	$256.70
Purchase #5	$42.49	6.852%	$45.4014	$45.40	$45.40	$45.40
Purchase #6	$26.72	7.480%	$28.7187	$28.72	$28.70	$28.70
Purchase #7	$51.31	6.377%	$54.582	$54.58	$54.60	$54.60
7 purchase totals =	$837.18		$902.8859	$902.89	$902.90	$902.90