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	$153.90	8.440%	$166.8892	$166.89	$166.90	$166.90
Purchase #2	$203.64	8.362%	$220.6684	$220.67	$220.65	$220.70
Purchase #3	$83.77	7.674%	$90.1985	$90.20	$90.20	$90.20
Purchase #4	$139.87	11.268%	$155.6306	$155.63	$155.65	$155.60
Purchase #5	$40.41	3.170%	$41.691	$41.69	$41.70	$41.70
Purchase #6	$93.34	11.648%	$104.2122	$104.21	$104.20	$104.20
Purchase #7	$216.85	3.245%	$223.8868	$223.89	$223.90	$223.90
7 purchase totals =	$931.78		$1,003.1767	$1,003.18	$1,003.20	$1,003.20