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	$175.61	7.165%	$188.1925	$188.19	$188.20	$188.20
Purchase #2	$20.91	9.273%	$22.849	$22.85	$22.85	$22.80
Purchase #3	$37.70	8.306%	$40.8314	$40.83	$40.85	$40.80
Purchase #4	$196.56	6.763%	$209.8534	$209.85	$209.85	$209.90
Purchase #5	$137.48	5.336%	$144.8159	$144.82	$144.80	$144.80
Purchase #6	$72.70	13.211%	$82.3044	$82.30	$82.30	$82.30
Purchase #7	$183.34	5.842%	$194.0507	$194.05	$194.05	$194.10
7 purchase totals =	$824.30		$882.8973	$882.89	$882.90	$882.90