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	$179.82	11.699%	$200.8571	$200.86	$200.85	$200.90
Purchase #2	$115.68	12.236%	$129.8346	$129.83	$129.85	$129.80
Purchase #3	$226.46	7.180%	$242.7198	$242.72	$242.70	$242.70
Purchase #4	$86.62	5.222%	$91.1433	$91.14	$91.15	$91.10
Purchase #5	$192.46	12.576%	$216.6638	$216.66	$216.65	$216.70
Purchase #6	$89.44	6.562%	$95.3091	$95.31	$95.30	$95.30
Purchase #7	$55.98	10.115%	$61.6424	$61.64	$61.65	$61.60
7 purchase totals =	$946.46		$1,038.1701	$1,038.16	$1,038.15	$1,038.10