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	$137.73	5.263%	$144.9787	$144.98	$145.00	$145.00
Purchase #2	$200.82	9.190%	$219.2754	$219.28	$219.30	$219.30
Purchase #3	$117.78	10.651%	$130.3247	$130.32	$130.30	$130.30
Purchase #4	$101.89	10.489%	$112.5772	$112.58	$112.60	$112.60
Purchase #5	$227.36	5.456%	$239.7648	$239.76	$239.75	$239.80
Purchase #6	$62.49	13.835%	$71.1355	$71.14	$71.15	$71.10
Purchase #7	$113.78	8.452%	$123.3967	$123.40	$123.40	$123.40
7 purchase totals =	$961.85		$1,041.4530	$1,041.46	$1,041.50	$1,041.50