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	$41.79	8.720%	$45.4341	$45.43	$45.45	$45.40
Purchase #2	$162.53	11.311%	$180.9138	$180.91	$180.90	$180.90
Purchase #3	$242.55	12.102%	$271.9034	$271.90	$271.90	$271.90
Purchase #4	$206.72	12.362%	$232.2747	$232.27	$232.25	$232.30
Purchase #5	$40.90	4.832%	$42.8763	$42.88	$42.90	$42.90
Purchase #6	$63.90	6.287%	$67.9174	$67.92	$67.90	$67.90
Purchase #7	$83.87	3.158%	$86.5186	$86.52	$86.50	$86.50
7 purchase totals =	$842.26		$927.8383	$927.83	$927.80	$927.80