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	$46.35	13.489%	$52.6022	$52.60	$52.60	$52.60
Purchase #2	$74.98	11.722%	$83.7692	$83.77	$83.75	$83.80
Purchase #3	$161.64	7.851%	$174.3304	$174.33	$174.35	$174.30
Purchase #4	$65.52	12.480%	$73.6969	$73.70	$73.70	$73.70
Purchase #5	$180.81	5.515%	$190.7817	$190.78	$190.80	$190.80
Purchase #6	$67.25	7.160%	$72.0651	$72.07	$72.05	$72.10
Purchase #7	$30.54	3.450%	$31.5936	$31.59	$31.60	$31.60
7 purchase totals =	$627.09		$678.8391	$678.84	$678.85	$678.90