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	$123.57	3.304%	$127.6528	$127.65	$127.65	$127.70
Purchase #2	$178.54	12.264%	$200.4361	$200.44	$200.45	$200.40
Purchase #3	$56.84	4.347%	$59.3108	$59.31	$59.30	$59.30
Purchase #4	$48.74	3.211%	$50.305	$50.31	$50.30	$50.30
Purchase #5	$32.48	11.815%	$36.3175	$36.32	$36.30	$36.30
Purchase #6	$208.26	4.672%	$217.9899	$217.99	$218.00	$218.00
Purchase #7	$113.90	13.355%	$129.1113	$129.11	$129.10	$129.10
7 purchase totals =	$762.33		$821.1234	$821.13	$821.10	$821.10