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	$182.98	12.155%	$205.2212	$205.22	$205.20	$205.20
Purchase #2	$153.55	10.207%	$169.2228	$169.22	$169.20	$169.20
Purchase #3	$72.46	11.593%	$80.8603	$80.86	$80.85	$80.90
Purchase #4	$160.77	12.155%	$180.3116	$180.31	$180.30	$180.30
Purchase #5	$30.35	3.740%	$31.4851	$31.49	$31.50	$31.50
Purchase #6	$78.89	11.602%	$88.0428	$88.04	$88.05	$88.00
Purchase #7	$239.56	7.427%	$257.3521	$257.35	$257.35	$257.40
7 purchase totals =	$918.56		$1,012.4959	$1,012.49	$1,012.45	$1,012.50