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	$132.62	3.476%	$137.2299	$137.23	$137.25	$137.20
Purchase #2	$78.67	4.575%	$82.2692	$82.27	$82.25	$82.30
Purchase #3	$84.58	9.524%	$92.6354	$92.64	$92.65	$92.60
Purchase #4	$243.75	11.785%	$272.4759	$272.48	$272.50	$272.50
Purchase #5	$37.78	10.362%	$41.6948	$41.69	$41.70	$41.70
Purchase #6	$107.76	6.378%	$114.6329	$114.63	$114.65	$114.60
Purchase #7	$219.50	9.410%	$240.155	$240.16	$240.15	$240.20
7 purchase totals =	$904.66		$981.0931	$981.10	$981.15	$981.10