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	$135.73	6.655%	$144.7628	$144.76	$144.75	$144.80
Purchase #2	$38.86	5.163%	$40.8663	$40.87	$40.85	$40.90
Purchase #3	$203.35	7.402%	$218.402	$218.40	$218.40	$218.40
Purchase #4	$91.25	5.157%	$95.9558	$95.96	$95.95	$96.00
Purchase #5	$140.36	3.745%	$145.6165	$145.62	$145.60	$145.60
Purchase #6	$118.78	7.588%	$127.793	$127.79	$127.80	$127.80
Purchase #7	$59.40	8.445%	$64.4163	$64.42	$64.40	$64.40
7 purchase totals =	$787.73		$837.8127	$837.82	$837.75	$837.90