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	$137.89	8.798%	$150.0216	$150.02	$150.00	$150.00
Purchase #2	$175.77	5.738%	$185.8557	$185.86	$185.85	$185.90
Purchase #3	$169.47	7.714%	$182.5429	$182.54	$182.55	$182.50
Purchase #4	$50.44	5.764%	$53.3474	$53.35	$53.35	$53.30
Purchase #5	$218.56	10.526%	$241.5656	$241.57	$241.55	$241.60
Purchase #6	$73.63	5.570%	$77.7312	$77.73	$77.75	$77.70
Purchase #7	$236.68	7.510%	$254.4547	$254.45	$254.45	$254.50
7 purchase totals =	$1,062.44		$1,145.5191	$1,145.52	$1,145.50	$1,145.50