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	$232.78	6.745%	$248.481	$248.48	$248.50	$248.50
Purchase #2	$189.59	6.864%	$202.6035	$202.60	$202.60	$202.60
Purchase #3	$122.78	6.748%	$131.0652	$131.07	$131.05	$131.10
Purchase #4	$117.30	11.441%	$130.7203	$130.72	$130.70	$130.70
Purchase #5	$100.51	10.779%	$111.344	$111.34	$111.35	$111.30
Purchase #6	$29.44	12.495%	$33.1185	$33.12	$33.10	$33.10
Purchase #7	$31.48	12.386%	$35.3791	$35.38	$35.40	$35.40
7 purchase totals =	$823.88		$892.7116	$892.71	$892.70	$892.70