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	$19.37	4.515%	$20.2446	$20.24	$20.25	$20.20
Purchase #2	$136.56	12.820%	$154.067	$154.07	$154.05	$154.10
Purchase #3	$85.80	3.792%	$89.0535	$89.05	$89.05	$89.10
Purchase #4	$178.31	12.436%	$200.4846	$200.48	$200.50	$200.50
Purchase #5	$59.61	5.798%	$63.0662	$63.07	$63.05	$63.10
Purchase #6	$153.83	13.675%	$174.8663	$174.87	$174.85	$174.90
Purchase #7	$250.63	9.470%	$274.3647	$274.36	$274.35	$274.40
7 purchase totals =	$884.11		$976.1469	$976.14	$976.10	$976.30