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	$107.52	11.801%	$120.2084	$120.21	$120.20	$120.20
Purchase #2	$173.43	10.462%	$191.5742	$191.57	$191.55	$191.60
Purchase #3	$166.73	11.455%	$185.8289	$185.83	$185.85	$185.80
Purchase #4	$78.56	8.244%	$85.0365	$85.04	$85.05	$85.00
Purchase #5	$180.75	11.727%	$201.9466	$201.95	$201.95	$201.90
Purchase #6	$82.80	10.501%	$91.4948	$91.49	$91.50	$91.50
Purchase #7	$78.48	11.258%	$87.3153	$87.32	$87.30	$87.30
7 purchase totals =	$868.27		$963.4047	$963.41	$963.40	$963.30