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	$81.58	4.235%	$85.0349	$85.03	$85.05	$85.00
Purchase #2	$67.94	4.813%	$71.21	$71.21	$71.20	$71.20
Purchase #3	$37.47	4.826%	$39.2783	$39.28	$39.30	$39.30
Purchase #4	$182.31	7.571%	$196.1127	$196.11	$196.10	$196.10
Purchase #5	$33.41	4.131%	$34.7902	$34.79	$34.80	$34.80
Purchase #6	$107.41	10.453%	$118.6376	$118.64	$118.65	$118.60
Purchase #7	$137.53	3.265%	$142.0204	$142.02	$142.00	$142.00
7 purchase totals =	$647.65		$687.0841	$687.08	$687.10	$687.00