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	$136.95	12.196%	$153.6524	$153.65	$153.65	$153.70
Purchase #2	$55.96	13.285%	$63.3943	$63.39	$63.40	$63.40
Purchase #3	$65.67	11.646%	$73.3179	$73.32	$73.30	$73.30
Purchase #4	$154.89	13.450%	$175.7227	$175.72	$175.70	$175.70
Purchase #5	$95.25	4.601%	$99.6325	$99.63	$99.65	$99.60
Purchase #6	$39.46	6.758%	$42.1267	$42.13	$42.15	$42.10
Purchase #7	$192.66	6.685%	$205.5393	$205.54	$205.55	$205.50
7 purchase totals =	$740.84		$813.3858	$813.38	$813.40	$813.30