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	$71.32	11.222%	$79.3235	$79.32	$79.30	$79.30
Purchase #2	$127.51	6.599%	$135.9244	$135.92	$135.90	$135.90
Purchase #3	$100.74	4.251%	$105.0225	$105.02	$105.00	$105.00
Purchase #4	$226.92	4.360%	$236.8137	$236.81	$236.80	$236.80
Purchase #5	$30.46	6.628%	$32.4789	$32.48	$32.50	$32.50
Purchase #6	$133.90	5.165%	$140.8159	$140.82	$140.80	$140.80
Purchase #7	$77.82	9.659%	$85.3366	$85.34	$85.35	$85.30
7 purchase totals =	$768.67		$815.7155	$815.71	$815.65	$815.60