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	$36.72	8.570%	$39.8669	$39.87	$39.85	$39.90
Purchase #2	$187.98	11.792%	$210.1466	$210.15	$210.15	$210.10
Purchase #3	$147.31	13.267%	$166.8536	$166.85	$166.85	$166.90
Purchase #4	$191.27	10.711%	$211.7569	$211.76	$211.75	$211.80
Purchase #5	$129.50	6.488%	$137.902	$137.90	$137.90	$137.90
Purchase #6	$86.97	3.489%	$90.0044	$90.00	$90.00	$90.00
Purchase #7	$201.27	11.590%	$224.5972	$224.60	$224.60	$224.60
7 purchase totals =	$981.02		$1,081.1276	$1,081.13	$1,081.10	$1,081.20