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	$204.58	12.534%	$230.2221	$230.22	$230.20	$230.20
Purchase #2	$168.84	10.274%	$186.1866	$186.19	$186.20	$186.20
Purchase #3	$232.82	3.301%	$240.5054	$240.51	$240.50	$240.50
Purchase #4	$86.59	4.129%	$90.1653	$90.17	$90.15	$90.20
Purchase #5	$183.32	4.450%	$191.4777	$191.48	$191.50	$191.50
Purchase #6	$247.81	9.524%	$271.4114	$271.41	$271.40	$271.40
Purchase #7	$170.93	10.495%	$188.8691	$188.87	$188.85	$188.90
7 purchase totals =	$1,294.89		$1,398.8376	$1,398.85	$1,398.80	$1,398.90