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	$92.49	7.294%	$99.2362	$99.24	$99.25	$99.20
Purchase #2	$139.66	9.449%	$152.8565	$152.86	$152.85	$152.90
Purchase #3	$91.51	9.533%	$100.2336	$100.23	$100.25	$100.20
Purchase #4	$104.84	6.467%	$111.62	$111.62	$111.60	$111.60
Purchase #5	$80.63	11.155%	$89.6243	$89.62	$89.60	$89.60
Purchase #6	$191.92	5.344%	$202.1762	$202.18	$202.20	$202.20
Purchase #7	$79.44	6.318%	$84.459	$84.46	$84.45	$84.50
7 purchase totals =	$780.49		$840.2058	$840.21	$840.20	$840.20