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	$99.64	10.318%	$109.9209	$109.92	$109.90	$109.90
Purchase #2	$91.84	3.260%	$94.834	$94.83	$94.85	$94.80
Purchase #3	$89.51	5.384%	$94.3292	$94.33	$94.35	$94.30
Purchase #4	$140.40	11.455%	$156.4828	$156.48	$156.50	$156.50
Purchase #5	$211.41	5.357%	$222.7352	$222.74	$222.75	$222.70
Purchase #6	$184.57	5.259%	$194.2765	$194.28	$194.30	$194.30
Purchase #7	$56.33	6.868%	$60.1987	$60.20	$60.20	$60.20
7 purchase totals =	$873.70		$932.7773	$932.78	$932.85	$932.70