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	$156.29	10.410%	$172.5598	$172.56	$172.55	$172.60
Purchase #2	$243.33	10.155%	$268.0402	$268.04	$268.05	$268.00
Purchase #3	$75.67	3.610%	$78.4017	$78.40	$78.40	$78.40
Purchase #4	$62.55	9.167%	$68.284	$68.28	$68.30	$68.30
Purchase #5	$83.30	9.113%	$90.8911	$90.89	$90.90	$90.90
Purchase #6	$109.73	7.241%	$117.6755	$117.68	$117.70	$117.70
Purchase #7	$29.40	9.310%	$32.1371	$32.14	$32.15	$32.10
7 purchase totals =	$760.27		$827.9894	$827.99	$828.05	$828.00