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	$29.28	13.442%	$33.2158	$33.22	$33.20	$33.20
Purchase #2	$137.60	10.787%	$152.4429	$152.44	$152.45	$152.40
Purchase #3	$178.37	6.216%	$189.4575	$189.46	$189.45	$189.50
Purchase #4	$115.51	4.670%	$120.9043	$120.90	$120.90	$120.90
Purchase #5	$39.47	4.307%	$41.17	$41.17	$41.15	$41.20
Purchase #6	$182.57	7.822%	$196.8506	$196.85	$196.85	$196.90
Purchase #7	$174.80	3.205%	$180.4023	$180.40	$180.40	$180.40
7 purchase totals =	$857.60		$914.4434	$914.44	$914.40	$914.50