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	$51.49	7.725%	$55.4676	$55.47	$55.45	$55.50
Purchase #2	$225.51	8.716%	$245.1655	$245.17	$245.15	$245.20
Purchase #3	$134.57	4.391%	$140.479	$140.48	$140.50	$140.50
Purchase #4	$75.60	9.442%	$82.7382	$82.74	$82.75	$82.70
Purchase #5	$57.72	4.784%	$60.4813	$60.48	$60.50	$60.50
Purchase #6	$187.74	7.722%	$202.2373	$202.24	$202.25	$202.20
Purchase #7	$199.98	11.155%	$222.2878	$222.29	$222.30	$222.30
7 purchase totals =	$932.61		$1,008.8567	$1,008.87	$1,008.90	$1,008.90