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	$131.58	10.637%	$145.5762	$145.58	$145.60	$145.60
Purchase #2	$90.90	3.250%	$93.8543	$93.85	$93.85	$93.90
Purchase #3	$237.73	12.870%	$268.3259	$268.33	$268.35	$268.30
Purchase #4	$102.52	6.402%	$109.0833	$109.08	$109.10	$109.10
Purchase #5	$207.28	12.157%	$232.479	$232.48	$232.50	$232.50
Purchase #6	$228.68	11.383%	$254.7106	$254.71	$254.70	$254.70
Purchase #7	$178.83	9.625%	$196.0424	$196.04	$196.05	$196.00
7 purchase totals =	$1,177.52		$1,300.0717	$1,300.07	$1,300.15	$1,300.10