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	$82.90	6.488%	$88.2786	$88.28	$88.30	$88.30
Purchase #2	$97.77	12.370%	$109.8641	$109.86	$109.85	$109.90
Purchase #3	$171.52	5.483%	$180.9244	$180.92	$180.90	$180.90
Purchase #4	$54.28	10.488%	$59.9729	$59.97	$59.95	$60.00
Purchase #5	$96.82	13.340%	$109.7358	$109.74	$109.75	$109.70
Purchase #6	$31.52	9.794%	$34.6071	$34.61	$34.60	$34.60
Purchase #7	$69.58	5.392%	$73.3318	$73.33	$73.35	$73.30
7 purchase totals =	$604.39		$656.7147	$656.71	$656.70	$656.70