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	$154.48	11.778%	$172.6747	$172.67	$172.65	$172.70
Purchase #2	$15.88	13.782%	$18.0686	$18.07	$18.05	$18.10
Purchase #3	$195.93	10.410%	$216.3263	$216.33	$216.35	$216.30
Purchase #4	$180.61	7.850%	$194.7879	$194.79	$194.80	$194.80
Purchase #5	$54.25	12.759%	$61.1718	$61.17	$61.15	$61.20
Purchase #6	$167.28	9.520%	$183.2051	$183.21	$183.20	$183.20
Purchase #7	$245.46	3.421%	$253.8572	$253.86	$253.85	$253.90
7 purchase totals =	$1,013.89		$1,100.0916	$1,100.10	$1,100.05	$1,100.20