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	$88.72	13.156%	$100.392	$100.39	$100.40	$100.40
Purchase #2	$37.34	11.519%	$41.6412	$41.64	$41.65	$41.60
Purchase #3	$54.77	9.388%	$59.9118	$59.91	$59.90	$59.90
Purchase #4	$32.55	6.202%	$34.5688	$34.57	$34.55	$34.60
Purchase #5	$247.77	9.324%	$270.8721	$270.87	$270.85	$270.90
Purchase #6	$76.90	5.279%	$80.9596	$80.96	$80.95	$81.00
Purchase #7	$164.28	12.517%	$184.8429	$184.84	$184.85	$184.80
7 purchase totals =	$702.33		$773.1884	$773.18	$773.15	$773.20