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	$77.31	7.218%	$82.8902	$82.89	$82.90	$82.90
Purchase #2	$32.52	8.334%	$35.2302	$35.23	$35.25	$35.20
Purchase #3	$175.88	7.265%	$188.6577	$188.66	$188.65	$188.70
Purchase #4	$33.35	9.536%	$36.5303	$36.53	$36.55	$36.50
Purchase #5	$212.68	9.512%	$232.9101	$232.91	$232.90	$232.90
Purchase #6	$118.54	7.416%	$127.3309	$127.33	$127.35	$127.30
Purchase #7	$133.85	12.265%	$150.2667	$150.27	$150.25	$150.30
7 purchase totals =	$784.13		$853.8161	$853.82	$853.85	$853.80