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	$88.49	13.550%	$100.4804	$100.48	$100.50	$100.50
Purchase #2	$231.42	12.302%	$259.8893	$259.89	$259.90	$259.90
Purchase #3	$215.62	11.556%	$240.537	$240.54	$240.55	$240.50
Purchase #4	$199.29	4.446%	$208.1504	$208.15	$208.15	$208.20
Purchase #5	$176.63	7.427%	$189.7483	$189.75	$189.75	$189.70
Purchase #6	$54.67	4.233%	$56.9842	$56.98	$57.00	$57.00
Purchase #7	$216.75	12.145%	$243.0743	$243.07	$243.05	$243.10
7 purchase totals =	$1,182.87		$1,298.8639	$1,298.86	$1,298.90	$1,298.90