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	$70.46	8.288%	$76.2997	$76.30	$76.30	$76.30
Purchase #2	$124.48	12.179%	$139.6404	$139.64	$139.65	$139.60
Purchase #3	$103.34	7.753%	$111.352	$111.35	$111.35	$111.40
Purchase #4	$30.57	11.313%	$34.0284	$34.03	$34.05	$34.00
Purchase #5	$96.38	13.213%	$109.1147	$109.11	$109.10	$109.10
Purchase #6	$200.80	11.765%	$224.4241	$224.42	$224.40	$224.40
Purchase #7	$151.79	7.336%	$162.9253	$162.93	$162.95	$162.90
7 purchase totals =	$777.82		$857.7846	$857.78	$857.80	$857.70