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	$33.38	13.765%	$37.9748	$37.97	$37.95	$38.00
Purchase #2	$102.33	8.637%	$111.1682	$111.17	$111.15	$111.20
Purchase #3	$179.77	3.191%	$185.5065	$185.51	$185.50	$185.50
Purchase #4	$141.66	12.587%	$159.4907	$159.49	$159.50	$159.50
Purchase #5	$29.28	7.132%	$31.3682	$31.37	$31.35	$31.40
Purchase #6	$127.76	11.297%	$142.193	$142.19	$142.20	$142.20
Purchase #7	$185.38	12.278%	$208.141	$208.14	$208.15	$208.10
7 purchase totals =	$799.56		$875.8424	$875.84	$875.80	$875.90