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	$209.76	6.202%	$222.7693	$222.77	$222.75	$222.80
Purchase #2	$197.84	12.299%	$222.1723	$222.17	$222.15	$222.20
Purchase #3	$247.63	12.339%	$278.1851	$278.19	$278.20	$278.20
Purchase #4	$25.89	12.401%	$29.1006	$29.10	$29.10	$29.10
Purchase #5	$173.62	10.127%	$191.2025	$191.20	$191.20	$191.20
Purchase #6	$59.94	12.295%	$67.3096	$67.31	$67.30	$67.30
Purchase #7	$82.75	8.442%	$89.7358	$89.74	$89.75	$89.70
7 purchase totals =	$997.43		$1,100.4752	$1,100.48	$1,100.45	$1,100.50