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	$156.66	7.371%	$168.2074	$168.21	$168.20	$168.20
Purchase #2	$127.86	11.339%	$142.358	$142.36	$142.35	$142.40
Purchase #3	$31.40	4.382%	$32.7759	$32.78	$32.80	$32.80
Purchase #4	$151.99	9.759%	$166.8227	$166.82	$166.80	$166.80
Purchase #5	$106.63	4.327%	$111.2439	$111.24	$111.25	$111.20
Purchase #6	$155.88	6.774%	$166.4393	$166.44	$166.45	$166.40
Purchase #7	$221.48	10.159%	$243.9802	$243.98	$244.00	$244.00
7 purchase totals =	$951.90		$1,031.8274	$1,031.83	$1,031.85	$1,031.80