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	$65.64	10.425%	$72.483	$72.48	$72.50	$72.50
Purchase #2	$123.78	13.147%	$140.0534	$140.05	$140.05	$140.10
Purchase #3	$209.26	13.806%	$238.1504	$238.15	$238.15	$238.20
Purchase #4	$93.77	11.159%	$104.2338	$104.23	$104.25	$104.20
Purchase #5	$5.43	10.314%	$5.9901	$5.99	$6.00	$6.00
Purchase #6	$199.27	11.627%	$222.4391	$222.44	$222.45	$222.40
Purchase #7	$175.82	9.145%	$191.8987	$191.90	$191.90	$191.90
7 purchase totals =	$872.97		$975.2485	$975.24	$975.30	$975.30