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	$55.70	6.867%	$59.5249	$59.52	$59.50	$59.50
Purchase #2	$97.97	10.806%	$108.5566	$108.56	$108.55	$108.60
Purchase #3	$227.26	10.330%	$250.736	$250.74	$250.75	$250.70
Purchase #4	$63.85	12.752%	$71.9922	$71.99	$72.00	$72.00
Purchase #5	$241.47	13.399%	$273.8246	$273.82	$273.80	$273.80
Purchase #6	$150.61	11.570%	$168.0356	$168.04	$168.05	$168.00
Purchase #7	$43.93	4.342%	$45.8374	$45.84	$45.85	$45.80
7 purchase totals =	$880.79		$978.5073	$978.51	$978.50	$978.40