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	$156.56	5.502%	$165.1739	$165.17	$165.15	$165.20
Purchase #2	$237.34	13.846%	$270.2021	$270.20	$270.20	$270.20
Purchase #3	$226.34	10.524%	$250.16	$250.16	$250.15	$250.20
Purchase #4	$89.76	7.419%	$96.4193	$96.42	$96.40	$96.40
Purchase #5	$90.77	11.200%	$100.9362	$100.94	$100.95	$100.90
Purchase #6	$162.34	7.874%	$175.1227	$175.12	$175.10	$175.10
Purchase #7	$37.81	10.241%	$41.6821	$41.68	$41.70	$41.70
7 purchase totals =	$1,000.92		$1,099.6963	$1,099.69	$1,099.65	$1,099.70