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	$134.89	4.642%	$141.1516	$141.15	$141.15	$141.20
Purchase #2	$82.84	3.441%	$85.6905	$85.69	$85.70	$85.70
Purchase #3	$76.52	8.174%	$82.7747	$82.77	$82.75	$82.80
Purchase #4	$24.87	13.248%	$28.1648	$28.16	$28.15	$28.20
Purchase #5	$239.33	6.574%	$255.0636	$255.06	$255.05	$255.10
Purchase #6	$73.25	13.595%	$83.2083	$83.21	$83.20	$83.20
Purchase #7	$136.74	7.347%	$146.7863	$146.79	$146.80	$146.80
7 purchase totals =	$768.44		$822.8398	$822.83	$822.80	$823.00