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	$79.86	11.569%	$89.099	$89.10	$89.10	$89.10
Purchase #2	$191.35	5.201%	$201.3021	$201.30	$201.30	$201.30
Purchase #3	$228.89	8.411%	$248.1419	$248.14	$248.15	$248.10
Purchase #4	$67.26	13.797%	$76.5399	$76.54	$76.55	$76.50
Purchase #5	$97.61	7.792%	$105.2158	$105.22	$105.20	$105.20
Purchase #6	$243.98	11.165%	$271.2204	$271.22	$271.20	$271.20
Purchase #7	$59.57	10.540%	$65.8487	$65.85	$65.85	$65.80
7 purchase totals =	$968.52		$1,057.3678	$1,057.37	$1,057.35	$1,057.20