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	$250.65	9.381%	$274.1635	$274.16	$274.15	$274.20
Purchase #2	$80.46	11.716%	$89.8867	$89.89	$89.90	$89.90
Purchase #3	$161.35	11.294%	$179.5729	$179.57	$179.55	$179.60
Purchase #4	$118.26	7.579%	$127.2229	$127.22	$127.20	$127.20
Purchase #5	$61.82	3.163%	$63.7754	$63.78	$63.80	$63.80
Purchase #6	$154.57	13.584%	$175.5668	$175.57	$175.55	$175.60
Purchase #7	$199.67	8.779%	$217.199	$217.20	$217.20	$217.20
7 purchase totals =	$1,026.78		$1,127.3872	$1,127.39	$1,127.35	$1,127.50