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	$220.62	6.300%	$234.5191	$234.52	$234.50	$234.50
Purchase #2	$151.66	7.388%	$162.8646	$162.86	$162.85	$162.90
Purchase #3	$170.89	8.360%	$185.1764	$185.18	$185.20	$185.20
Purchase #4	$37.94	8.355%	$41.1099	$41.11	$41.10	$41.10
Purchase #5	$202.41	11.551%	$225.7904	$225.79	$225.80	$225.80
Purchase #6	$196.57	10.132%	$216.4865	$216.49	$216.50	$216.50
Purchase #7	$188.72	10.679%	$208.8734	$208.87	$208.85	$208.90
7 purchase totals =	$1,168.81		$1,274.8203	$1,274.82	$1,274.80	$1,274.90