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	$134.50	7.728%	$144.8942	$144.89	$144.90	$144.90
Purchase #2	$89.67	8.498%	$97.2902	$97.29	$97.30	$97.30
Purchase #3	$32.66	13.869%	$37.1896	$37.19	$37.20	$37.20
Purchase #4	$32.54	11.738%	$36.3595	$36.36	$36.35	$36.40
Purchase #5	$196.36	7.729%	$211.5367	$211.54	$211.55	$211.50
Purchase #6	$175.72	8.580%	$190.7968	$190.80	$190.80	$190.80
Purchase #7	$29.49	12.637%	$33.2167	$33.22	$33.20	$33.20
7 purchase totals =	$690.94		$751.2837	$751.29	$751.30	$751.30