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	$245.99	13.120%	$278.2639	$278.26	$278.25	$278.30
Purchase #2	$225.88	8.745%	$245.6332	$245.63	$245.65	$245.60
Purchase #3	$30.65	6.244%	$32.5638	$32.56	$32.55	$32.60
Purchase #4	$158.74	13.294%	$179.8429	$179.84	$179.85	$179.80
Purchase #5	$98.67	10.494%	$109.0244	$109.02	$109.00	$109.00
Purchase #6	$144.87	5.444%	$152.7567	$152.76	$152.75	$152.80
Purchase #7	$152.56	7.711%	$164.3239	$164.32	$164.30	$164.30
7 purchase totals =	$1,057.36		$1,162.4088	$1,162.39	$1,162.35	$1,162.40