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	$249.43	11.105%	$277.1292	$277.13	$277.15	$277.10
Purchase #2	$208.82	4.793%	$218.8287	$218.83	$218.85	$218.80
Purchase #3	$247.96	11.246%	$275.8456	$275.85	$275.85	$275.80
Purchase #4	$159.92	12.780%	$180.3578	$180.36	$180.35	$180.40
Purchase #5	$160.91	4.705%	$168.4808	$168.48	$168.50	$168.50
Purchase #6	$29.73	11.550%	$33.1638	$33.16	$33.15	$33.20
Purchase #7	$204.46	6.279%	$217.298	$217.30	$217.30	$217.30
7 purchase totals =	$1,261.23		$1,371.1039	$1,371.11	$1,371.15	$1,371.10