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	$154.63	10.684%	$171.1507	$171.15	$171.15	$171.20
Purchase #2	$43.64	7.176%	$46.7716	$46.77	$46.75	$46.80
Purchase #3	$101.36	10.345%	$111.8457	$111.85	$111.85	$111.80
Purchase #4	$20.71	6.817%	$22.1218	$22.12	$22.10	$22.10
Purchase #5	$77.48	5.705%	$81.9002	$81.90	$81.90	$81.90
Purchase #6	$52.55	5.453%	$55.4156	$55.42	$55.40	$55.40
Purchase #7	$218.40	9.443%	$239.0235	$239.02	$239.00	$239.00
7 purchase totals =	$668.77		$728.2291	$728.23	$728.15	$728.20