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	$172.31	9.312%	$188.3555	$188.36	$188.35	$188.40
Purchase #2	$229.61	13.608%	$260.8553	$260.86	$260.85	$260.90
Purchase #3	$111.92	10.830%	$124.0409	$124.04	$124.05	$124.00
Purchase #4	$101.34	3.717%	$105.1068	$105.11	$105.10	$105.10
Purchase #5	$140.31	10.392%	$154.891	$154.89	$154.90	$154.90
Purchase #6	$63.71	12.617%	$71.7483	$71.75	$71.75	$71.70
Purchase #7	$156.47	5.477%	$165.0399	$165.04	$165.05	$165.00
7 purchase totals =	$975.67		$1,070.0377	$1,070.05	$1,070.05	$1,070.00