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	$138.46	12.849%	$156.2507	$156.25	$156.25	$156.30
Purchase #2	$233.66	8.371%	$253.2197	$253.22	$253.20	$253.20
Purchase #3	$225.94	4.413%	$235.9107	$235.91	$235.90	$235.90
Purchase #4	$205.57	4.655%	$215.1393	$215.14	$215.15	$215.10
Purchase #5	$148.44	12.298%	$166.6952	$166.70	$166.70	$166.70
Purchase #6	$195.41	13.832%	$222.4391	$222.44	$222.45	$222.40
Purchase #7	$40.83	12.206%	$45.8137	$45.81	$45.80	$45.80
7 purchase totals =	$1,188.31		$1,295.4684	$1,295.47	$1,295.45	$1,295.40