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	$97.61	12.562%	$109.8718	$109.87	$109.85	$109.90
Purchase #2	$245.58	7.516%	$264.0378	$264.04	$264.05	$264.00
Purchase #3	$100.60	11.486%	$112.1549	$112.15	$112.15	$112.20
Purchase #4	$145.78	3.446%	$150.8036	$150.80	$150.80	$150.80
Purchase #5	$50.79	11.385%	$56.5724	$56.57	$56.55	$56.60
Purchase #6	$51.70	8.621%	$56.1571	$56.16	$56.15	$56.20
Purchase #7	$115.89	13.221%	$131.2118	$131.21	$131.20	$131.20
7 purchase totals =	$807.95		$880.8094	$880.80	$880.75	$880.90