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	$217.88	13.586%	$247.4812	$247.48	$247.50	$247.50
Purchase #2	$108.86	8.822%	$118.4636	$118.46	$118.45	$118.50
Purchase #3	$37.43	13.310%	$42.4119	$42.41	$42.40	$42.40
Purchase #4	$204.67	3.593%	$212.0238	$212.02	$212.00	$212.00
Purchase #5	$169.56	11.117%	$188.41	$188.41	$188.40	$188.40
Purchase #6	$5.93	3.470%	$6.1358	$6.14	$6.15	$6.10
Purchase #7	$196.51	9.556%	$215.2885	$215.29	$215.30	$215.30
7 purchase totals =	$940.84		$1,030.2148	$1,030.21	$1,030.20	$1,030.20