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	$110.54	11.740%	$123.5174	$123.52	$123.50	$123.50
Purchase #2	$196.75	11.390%	$219.1598	$219.16	$219.15	$219.20
Purchase #3	$56.35	9.391%	$61.6418	$61.64	$61.65	$61.60
Purchase #4	$183.64	3.315%	$189.7277	$189.73	$189.75	$189.70
Purchase #5	$81.50	4.680%	$85.3142	$85.31	$85.30	$85.30
Purchase #6	$196.47	3.739%	$203.816	$203.82	$203.80	$203.80
Purchase #7	$33.86	12.312%	$38.0288	$38.03	$38.05	$38.00
7 purchase totals =	$859.11		$921.2057	$921.21	$921.20	$921.10