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	$250.66	12.640%	$282.3434	$282.34	$282.35	$282.30
Purchase #2	$218.88	7.267%	$234.786	$234.79	$234.80	$234.80
Purchase #3	$92.70	9.661%	$101.6557	$101.66	$101.65	$101.70
Purchase #4	$83.29	13.143%	$94.2368	$94.24	$94.25	$94.20
Purchase #5	$50.62	6.443%	$53.8814	$53.88	$53.90	$53.90
Purchase #6	$54.28	11.392%	$60.4636	$60.46	$60.45	$60.50
Purchase #7	$182.50	7.650%	$196.4613	$196.46	$196.45	$196.50
7 purchase totals =	$932.93		$1,023.8282	$1,023.83	$1,023.85	$1,023.90