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	$29.42	3.771%	$30.5294	$30.53	$30.55	$30.50
Purchase #2	$71.48	9.793%	$78.48	$78.48	$78.50	$78.50
Purchase #3	$169.34	8.840%	$184.3097	$184.31	$184.30	$184.30
Purchase #4	$39.84	6.142%	$42.287	$42.29	$42.30	$42.30
Purchase #5	$155.57	9.372%	$170.15	$170.15	$170.15	$170.20
Purchase #6	$174.87	13.751%	$198.9164	$198.92	$198.90	$198.90
Purchase #7	$38.83	9.664%	$42.5825	$42.58	$42.60	$42.60
7 purchase totals =	$679.35		$747.2550	$747.26	$747.30	$747.30