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	$73.93	6.779%	$78.9417	$78.94	$78.95	$78.90
Purchase #2	$110.68	9.142%	$120.7984	$120.80	$120.80	$120.80
Purchase #3	$6.98	4.459%	$7.2912	$7.29	$7.30	$7.30
Purchase #4	$43.82	12.410%	$49.2581	$49.26	$49.25	$49.30
Purchase #5	$79.55	10.420%	$87.8391	$87.84	$87.85	$87.80
Purchase #6	$51.40	11.413%	$57.2663	$57.27	$57.25	$57.30
Purchase #7	$238.32	11.608%	$265.9842	$265.98	$266.00	$266.00
7 purchase totals =	$604.68		$667.3790	$667.38	$667.40	$667.40