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	$56.84	4.528%	$59.4137	$59.41	$59.40	$59.40
Purchase #2	$35.32	5.157%	$37.1415	$37.14	$37.15	$37.10
Purchase #3	$141.64	6.464%	$150.7956	$150.80	$150.80	$150.80
Purchase #4	$245.82	8.698%	$267.2014	$267.20	$267.20	$267.20
Purchase #5	$58.51	11.124%	$65.0187	$65.02	$65.00	$65.00
Purchase #6	$85.76	4.261%	$89.4142	$89.41	$89.40	$89.40
Purchase #7	$242.54	6.449%	$258.1814	$258.18	$258.20	$258.20
7 purchase totals =	$866.43		$927.1665	$927.16	$927.15	$927.10