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	$131.60	6.236%	$139.8066	$139.81	$139.80	$139.80
Purchase #2	$150.91	10.799%	$167.2068	$167.21	$167.20	$167.20
Purchase #3	$147.30	3.137%	$151.9208	$151.92	$151.90	$151.90
Purchase #4	$102.52	6.468%	$109.151	$109.15	$109.15	$109.20
Purchase #5	$82.28	9.197%	$89.8473	$89.85	$89.85	$89.80
Purchase #6	$111.90	5.121%	$117.6304	$117.63	$117.65	$117.60
Purchase #7	$231.67	10.868%	$256.8479	$256.85	$256.85	$256.80
7 purchase totals =	$958.18		$1,032.4108	$1,032.42	$1,032.40	$1,032.30