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	$10.56	4.806%	$11.0675	$11.07	$11.05	$11.10
Purchase #2	$165.96	3.570%	$171.8848	$171.88	$171.90	$171.90
Purchase #3	$53.55	3.453%	$55.3991	$55.40	$55.40	$55.40
Purchase #4	$11.45	3.265%	$11.8238	$11.82	$11.80	$11.80
Purchase #5	$100.31	12.768%	$113.1176	$113.12	$113.10	$113.10
Purchase #6	$41.54	10.478%	$45.8926	$45.89	$45.90	$45.90
Purchase #7	$126.63	4.276%	$132.0447	$132.04	$132.05	$132.00
7 purchase totals =	$510.00		$541.2301	$541.22	$541.20	$541.20