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	$129.46	6.587%	$137.9875	$137.99	$138.00	$138.00
Purchase #2	$129.49	8.264%	$140.1911	$140.19	$140.20	$140.20
Purchase #3	$180.53	6.870%	$192.9324	$192.93	$192.95	$192.90
Purchase #4	$54.38	9.494%	$59.5428	$59.54	$59.55	$59.50
Purchase #5	$134.83	13.121%	$152.521	$152.52	$152.50	$152.50
Purchase #6	$80.48	11.168%	$89.468	$89.47	$89.45	$89.50
Purchase #7	$107.69	12.344%	$120.9833	$120.98	$121.00	$121.00
7 purchase totals =	$816.86		$893.6261	$893.62	$893.65	$893.60