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	$185.66	12.602%	$209.0569	$209.06	$209.05	$209.10
Purchase #2	$240.70	11.824%	$269.1604	$269.16	$269.15	$269.20
Purchase #3	$29.89	10.660%	$33.0763	$33.08	$33.10	$33.10
Purchase #4	$170.72	12.452%	$191.9781	$191.98	$192.00	$192.00
Purchase #5	$130.71	11.727%	$146.0384	$146.04	$146.05	$146.00
Purchase #6	$181.67	9.456%	$198.8487	$198.85	$198.85	$198.80
Purchase #7	$85.93	7.449%	$92.3309	$92.33	$92.35	$92.30
7 purchase totals =	$1,025.28		$1,140.4897	$1,140.50	$1,140.55	$1,140.50