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	$65.36	7.865%	$70.5006	$70.50	$70.50	$70.50
Purchase #2	$187.59	3.808%	$194.7334	$194.73	$194.75	$194.70
Purchase #3	$38.35	5.104%	$40.3074	$40.31	$40.30	$40.30
Purchase #4	$73.91	12.383%	$83.0623	$83.06	$83.05	$83.10
Purchase #5	$137.71	12.738%	$155.2515	$155.25	$155.25	$155.30
Purchase #6	$199.55	5.184%	$209.8947	$209.89	$209.90	$209.90
Purchase #7	$160.57	8.214%	$173.7592	$173.76	$173.75	$173.80
7 purchase totals =	$863.04		$927.5091	$927.50	$927.50	$927.60