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	$81.63	10.140%	$89.9073	$89.91	$89.90	$89.90
Purchase #2	$220.53	8.175%	$238.5583	$238.56	$238.55	$238.60
Purchase #3	$69.94	11.662%	$78.0964	$78.10	$78.10	$78.10
Purchase #4	$114.48	12.357%	$128.6263	$128.63	$128.65	$128.60
Purchase #5	$81.32	13.358%	$92.1827	$92.18	$92.20	$92.20
Purchase #6	$196.93	8.605%	$213.8758	$213.88	$213.90	$213.90
Purchase #7	$229.77	10.634%	$254.2037	$254.20	$254.20	$254.20
7 purchase totals =	$994.60		$1,095.4505	$1,095.46	$1,095.50	$1,095.50