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	$81.54	13.447%	$92.5047	$92.50	$92.50	$92.50
Purchase #2	$85.38	8.712%	$92.8183	$92.82	$92.80	$92.80
Purchase #3	$54.56	8.633%	$59.2702	$59.27	$59.25	$59.30
Purchase #4	$45.91	7.846%	$49.5121	$49.51	$49.50	$49.50
Purchase #5	$35.97	11.839%	$40.2285	$40.23	$40.25	$40.20
Purchase #6	$147.56	12.159%	$165.5018	$165.50	$165.50	$165.50
Purchase #7	$145.41	13.400%	$164.8949	$164.89	$164.90	$164.90
7 purchase totals =	$596.33		$664.7305	$664.72	$664.70	$664.70