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	$169.63	7.827%	$182.9069	$182.91	$182.90	$182.90
Purchase #2	$43.33	5.744%	$45.8189	$45.82	$45.80	$45.80
Purchase #3	$152.91	12.809%	$172.4962	$172.50	$172.50	$172.50
Purchase #4	$78.80	13.505%	$89.4419	$89.44	$89.45	$89.40
Purchase #5	$246.61	4.413%	$257.4929	$257.49	$257.50	$257.50
Purchase #6	$201.84	12.697%	$227.4676	$227.47	$227.45	$227.50
Purchase #7	$200.98	3.521%	$208.0565	$208.06	$208.05	$208.10
7 purchase totals =	$1,094.10		$1,183.6809	$1,183.69	$1,183.65	$1,183.70