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	$37.41	12.204%	$41.9755	$41.98	$42.00	$42.00
Purchase #2	$139.91	12.282%	$157.0937	$157.09	$157.10	$157.10
Purchase #3	$160.76	6.514%	$171.2319	$171.23	$171.25	$171.20
Purchase #4	$220.63	6.125%	$234.1436	$234.14	$234.15	$234.10
Purchase #5	$156.30	8.363%	$169.3714	$169.37	$169.35	$169.40
Purchase #6	$245.41	13.861%	$279.4263	$279.43	$279.45	$279.40
Purchase #7	$55.62	10.532%	$61.4779	$61.48	$61.50	$61.50
7 purchase totals =	$1,016.04		$1,114.7203	$1,114.72	$1,114.80	$1,114.70