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	$244.62	3.378%	$252.8833	$252.88	$252.90	$252.90
Purchase #2	$153.29	11.503%	$170.9229	$170.92	$170.90	$170.90
Purchase #3	$82.39	8.703%	$89.5604	$89.56	$89.55	$89.60
Purchase #4	$41.98	7.476%	$45.1184	$45.12	$45.10	$45.10
Purchase #5	$179.46	10.601%	$198.4846	$198.48	$198.50	$198.50
Purchase #6	$209.59	8.359%	$227.1096	$227.11	$227.10	$227.10
Purchase #7	$216.45	5.687%	$228.7595	$228.76	$228.75	$228.80
7 purchase totals =	$1,127.78		$1,212.8387	$1,212.83	$1,212.80	$1,212.90