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	$106.85	12.436%	$120.1379	$120.14	$120.15	$120.10
Purchase #2	$244.53	6.742%	$261.0162	$261.02	$261.00	$261.00
Purchase #3	$244.50	12.412%	$274.8473	$274.85	$274.85	$274.80
Purchase #4	$111.31	12.862%	$125.6267	$125.63	$125.65	$125.60
Purchase #5	$250.58	6.497%	$266.8602	$266.86	$266.85	$266.90
Purchase #6	$31.41	5.540%	$33.1501	$33.15	$33.15	$33.20
Purchase #7	$81.66	11.304%	$90.8908	$90.89	$90.90	$90.90
7 purchase totals =	$1,070.84		$1,172.5292	$1,172.54	$1,172.55	$1,172.50