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	$150.58	5.131%	$158.3063	$158.31	$158.30	$158.30
Purchase #2	$88.97	12.416%	$100.0165	$100.02	$100.00	$100.00
Purchase #3	$181.32	11.749%	$202.6233	$202.62	$202.60	$202.60
Purchase #4	$72.72	12.755%	$81.9954	$82.00	$82.00	$82.00
Purchase #5	$96.88	8.218%	$104.8416	$104.84	$104.85	$104.80
Purchase #6	$244.41	11.791%	$273.2284	$273.23	$273.25	$273.20
Purchase #7	$91.58	8.144%	$99.0383	$99.04	$99.05	$99.00
7 purchase totals =	$926.46		$1,020.0498	$1,020.06	$1,020.05	$1,019.90