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	$19.75	13.165%	$22.3501	$22.35	$22.35	$22.40
Purchase #2	$222.86	9.446%	$243.9114	$243.91	$243.90	$243.90
Purchase #3	$179.62	4.204%	$187.1712	$187.17	$187.15	$187.20
Purchase #4	$80.88	12.296%	$90.825	$90.83	$90.85	$90.80
Purchase #5	$250.37	3.597%	$259.3758	$259.38	$259.40	$259.40
Purchase #6	$155.58	9.550%	$170.4379	$170.44	$170.45	$170.40
Purchase #7	$105.76	9.714%	$116.0335	$116.03	$116.05	$116.00
7 purchase totals =	$1,014.82		$1,090.1049	$1,090.11	$1,090.15	$1,090.10