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	$78.58	5.515%	$82.9137	$82.91	$82.90	$82.90
Purchase #2	$213.55	12.415%	$240.0622	$240.06	$240.05	$240.10
Purchase #3	$187.91	10.607%	$207.8416	$207.84	$207.85	$207.80
Purchase #4	$214.54	7.592%	$230.8279	$230.83	$230.85	$230.80
Purchase #5	$59.91	13.716%	$68.1273	$68.13	$68.15	$68.10
Purchase #6	$63.89	11.331%	$71.1294	$71.13	$71.15	$71.10
Purchase #7	$191.33	13.483%	$217.127	$217.13	$217.15	$217.10
7 purchase totals =	$1,009.71		$1,118.0291	$1,118.03	$1,118.10	$1,117.90