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	$70.44	11.576%	$78.5941	$78.59	$78.60	$78.60
Purchase #2	$124.61	3.630%	$129.1333	$129.13	$129.15	$129.10
Purchase #3	$245.61	9.592%	$269.1689	$269.17	$269.15	$269.20
Purchase #4	$86.53	4.394%	$90.3321	$90.33	$90.35	$90.30
Purchase #5	$128.58	9.401%	$140.6678	$140.67	$140.65	$140.70
Purchase #6	$43.25	4.132%	$45.0371	$45.04	$45.05	$45.00
Purchase #7	$129.38	10.116%	$142.4681	$142.47	$142.45	$142.50
7 purchase totals =	$828.40		$895.4014	$895.40	$895.40	$895.40