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	$148.84	12.116%	$166.8735	$166.87	$166.85	$166.90
Purchase #2	$100.72	5.477%	$106.2364	$106.24	$106.25	$106.20
Purchase #3	$157.98	8.782%	$171.8538	$171.85	$171.85	$171.90
Purchase #4	$81.85	11.799%	$91.5075	$91.51	$91.50	$91.50
Purchase #5	$57.62	12.731%	$64.9556	$64.96	$64.95	$65.00
Purchase #6	$63.72	12.743%	$71.8398	$71.84	$71.85	$71.80
Purchase #7	$102.25	4.491%	$106.842	$106.84	$106.85	$106.80
7 purchase totals =	$712.98		$780.1086	$780.11	$780.10	$780.10