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	$83.51	3.575%	$86.4955	$86.50	$86.50	$86.50
Purchase #2	$122.89	13.765%	$139.8058	$139.81	$139.80	$139.80
Purchase #3	$91.31	6.853%	$97.5675	$97.57	$97.55	$97.60
Purchase #4	$85.44	10.736%	$94.6128	$94.61	$94.60	$94.60
Purchase #5	$108.66	11.760%	$121.4384	$121.44	$121.45	$121.40
Purchase #6	$82.73	7.773%	$89.1606	$89.16	$89.15	$89.20
Purchase #7	$193.73	13.152%	$219.2094	$219.21	$219.20	$219.20
7 purchase totals =	$768.27		$848.2900	$848.30	$848.25	$848.30