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	$123.92	3.588%	$128.3662	$128.37	$128.35	$128.40
Purchase #2	$221.78	4.144%	$230.9706	$230.97	$230.95	$231.00
Purchase #3	$39.90	11.282%	$44.4015	$44.40	$44.40	$44.40
Purchase #4	$91.67	8.559%	$99.516	$99.52	$99.50	$99.50
Purchase #5	$167.63	12.736%	$188.9794	$188.98	$189.00	$189.00
Purchase #6	$119.46	6.717%	$127.4841	$127.48	$127.50	$127.50
Purchase #7	$67.67	7.638%	$72.8386	$72.84	$72.85	$72.80
7 purchase totals =	$832.03		$892.5564	$892.56	$892.55	$892.60