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	$134.39	6.815%	$143.5487	$143.55	$143.55	$143.50
Purchase #2	$220.73	13.365%	$250.2306	$250.23	$250.25	$250.20
Purchase #3	$40.86	11.296%	$45.4755	$45.48	$45.50	$45.50
Purchase #4	$220.66	4.144%	$229.8042	$229.80	$229.80	$229.80
Purchase #5	$17.82	3.620%	$18.4651	$18.47	$18.45	$18.50
Purchase #6	$49.85	5.222%	$52.4532	$52.45	$52.45	$52.50
Purchase #7	$41.93	9.199%	$45.7871	$45.79	$45.80	$45.80
7 purchase totals =	$726.24		$785.7644	$785.77	$785.80	$785.80