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	$84.85	7.228%	$90.983	$90.98	$91.00	$91.00
Purchase #2	$204.78	9.194%	$223.6075	$223.61	$223.60	$223.60
Purchase #3	$153.69	10.343%	$169.5862	$169.59	$169.60	$169.60
Purchase #4	$159.30	6.229%	$169.2228	$169.22	$169.20	$169.20
Purchase #5	$97.26	9.540%	$106.5386	$106.54	$106.55	$106.50
Purchase #6	$192.70	12.121%	$216.0572	$216.06	$216.05	$216.10
Purchase #7	$212.73	9.559%	$233.0649	$233.06	$233.05	$233.10
7 purchase totals =	$1,105.31		$1,209.0602	$1,209.06	$1,209.05	$1,209.10