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	$52.58	8.423%	$57.0088	$57.01	$57.00	$57.00
Purchase #2	$136.70	10.785%	$151.4431	$151.44	$151.45	$151.40
Purchase #3	$229.97	10.848%	$254.9171	$254.92	$254.90	$254.90
Purchase #4	$149.34	3.319%	$154.2966	$154.30	$154.30	$154.30
Purchase #5	$59.93	12.504%	$67.4236	$67.42	$67.40	$67.40
Purchase #6	$242.55	5.484%	$255.8514	$255.85	$255.85	$255.90
Purchase #7	$215.54	13.394%	$244.4094	$244.41	$244.40	$244.40
7 purchase totals =	$1,086.61		$1,185.3500	$1,185.35	$1,185.30	$1,185.30