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	$121.64	8.618%	$132.1229	$132.12	$132.10	$132.10
Purchase #2	$150.36	10.868%	$166.7011	$166.70	$166.70	$166.70
Purchase #3	$44.63	11.799%	$49.8959	$49.90	$49.90	$49.90
Purchase #4	$198.43	12.655%	$223.5413	$223.54	$223.55	$223.50
Purchase #5	$80.28	13.170%	$90.8529	$90.85	$90.85	$90.90
Purchase #6	$91.92	9.806%	$100.9337	$100.93	$100.95	$100.90
Purchase #7	$130.34	6.800%	$139.2031	$139.20	$139.20	$139.20
7 purchase totals =	$817.60		$903.2509	$903.24	$903.25	$903.20