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	$74.92	10.817%	$83.0241	$83.02	$83.00	$83.00
Purchase #2	$160.76	7.227%	$172.3781	$172.38	$172.40	$172.40
Purchase #3	$219.59	10.442%	$242.5196	$242.52	$242.50	$242.50
Purchase #4	$98.35	11.273%	$109.437	$109.44	$109.45	$109.40
Purchase #5	$248.76	3.821%	$258.2651	$258.27	$258.25	$258.30
Purchase #6	$72.83	7.246%	$78.1073	$78.11	$78.10	$78.10
Purchase #7	$151.43	12.333%	$170.1059	$170.11	$170.10	$170.10
7 purchase totals =	$1,026.64		$1,113.8371	$1,113.85	$1,113.80	$1,113.80