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	$167.26	7.809%	$180.3213	$180.32	$180.30	$180.30
Purchase #2	$41.95	10.349%	$46.2914	$46.29	$46.30	$46.30
Purchase #3	$32.65	5.301%	$34.3808	$34.38	$34.40	$34.40
Purchase #4	$168.44	4.275%	$175.6408	$175.64	$175.65	$175.60
Purchase #5	$209.25	6.248%	$222.3239	$222.32	$222.30	$222.30
Purchase #6	$57.70	3.655%	$59.8089	$59.81	$59.80	$59.80
Purchase #7	$106.56	3.741%	$110.5464	$110.55	$110.55	$110.50
7 purchase totals =	$783.81		$829.3135	$829.31	$829.30	$829.20