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	$54.42	6.542%	$57.9802	$57.98	$58.00	$58.00
Purchase #2	$105.88	11.298%	$117.8423	$117.84	$117.85	$117.80
Purchase #3	$169.57	9.556%	$185.7741	$185.77	$185.75	$185.80
Purchase #4	$77.64	7.317%	$83.3209	$83.32	$83.30	$83.30
Purchase #5	$172.92	7.283%	$185.5138	$185.51	$185.50	$185.50
Purchase #6	$219.48	6.281%	$233.2655	$233.27	$233.25	$233.30
Purchase #7	$209.83	10.200%	$231.2327	$231.23	$231.25	$231.20
7 purchase totals =	$1,009.74		$1,094.9295	$1,094.92	$1,094.90	$1,094.90