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	$172.97	9.316%	$189.0839	$189.08	$189.10	$189.10
Purchase #2	$216.33	5.759%	$228.7884	$228.79	$228.80	$228.80
Purchase #3	$110.44	5.214%	$116.1983	$116.20	$116.20	$116.20
Purchase #4	$85.27	6.223%	$90.5764	$90.58	$90.60	$90.60
Purchase #5	$162.60	7.120%	$174.1771	$174.18	$174.20	$174.20
Purchase #6	$43.89	3.642%	$45.4885	$45.49	$45.50	$45.50
Purchase #7	$139.98	9.204%	$152.8638	$152.86	$152.85	$152.90
7 purchase totals =	$931.48		$997.1764	$997.18	$997.25	$997.30