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	$40.81	11.516%	$45.5097	$45.51	$45.50	$45.50
Purchase #2	$210.69	8.611%	$228.8325	$228.83	$228.85	$228.80
Purchase #3	$220.28	13.827%	$250.7381	$250.74	$250.75	$250.70
Purchase #4	$131.65	4.328%	$137.3478	$137.35	$137.35	$137.30
Purchase #5	$91.90	7.625%	$98.9074	$98.91	$98.90	$98.90
Purchase #6	$238.63	6.752%	$254.7423	$254.74	$254.75	$254.70
Purchase #7	$72.83	11.848%	$81.4589	$81.46	$81.45	$81.50
7 purchase totals =	$1,006.79		$1,097.5367	$1,097.54	$1,097.55	$1,097.40