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	$59.56	3.444%	$61.6112	$61.61	$61.60	$61.60
Purchase #2	$52.92	4.203%	$55.1442	$55.14	$55.15	$55.10
Purchase #3	$80.29	9.865%	$88.2106	$88.21	$88.20	$88.20
Purchase #4	$222.77	4.242%	$232.2199	$232.22	$232.20	$232.20
Purchase #5	$28.42	13.816%	$32.3465	$32.35	$32.35	$32.30
Purchase #6	$39.72	9.794%	$43.6102	$43.61	$43.60	$43.60
Purchase #7	$42.48	6.413%	$45.2042	$45.20	$45.20	$45.20
7 purchase totals =	$526.16		$558.3468	$558.34	$558.30	$558.20