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	$48.85	9.510%	$53.4956	$53.50	$53.50	$53.50
Purchase #2	$155.59	11.110%	$172.876	$172.88	$172.90	$172.90
Purchase #3	$138.77	9.750%	$152.3001	$152.30	$152.30	$152.30
Purchase #4	$116.64	6.296%	$123.9837	$123.98	$124.00	$124.00
Purchase #5	$200.92	11.799%	$224.6266	$224.63	$224.65	$224.60
Purchase #6	$109.50	6.703%	$116.8398	$116.84	$116.85	$116.80
Purchase #7	$36.69	7.779%	$39.5441	$39.54	$39.55	$39.50
7 purchase totals =	$806.96		$883.6659	$883.67	$883.75	$883.60