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	$197.56	3.394%	$204.2652	$204.27	$204.25	$204.30
Purchase #2	$75.44	13.840%	$85.8809	$85.88	$85.90	$85.90
Purchase #3	$64.74	9.251%	$70.7291	$70.73	$70.75	$70.70
Purchase #4	$14.69	5.524%	$15.5015	$15.50	$15.50	$15.50
Purchase #5	$148.89	5.103%	$156.4879	$156.49	$156.50	$156.50
Purchase #6	$56.50	8.532%	$61.3206	$61.32	$61.30	$61.30
Purchase #7	$41.90	13.825%	$47.6927	$47.69	$47.70	$47.70
7 purchase totals =	$599.72		$641.8779	$641.88	$641.90	$641.90