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	$36.26	3.328%	$37.4667	$37.47	$37.45	$37.50
Purchase #2	$131.64	4.274%	$137.2663	$137.27	$137.25	$137.30
Purchase #3	$100.54	8.700%	$109.287	$109.29	$109.30	$109.30
Purchase #4	$152.53	3.566%	$157.9692	$157.97	$157.95	$158.00
Purchase #5	$90.93	5.790%	$96.1948	$96.19	$96.20	$96.20
Purchase #6	$30.72	4.311%	$32.0443	$32.04	$32.05	$32.00
Purchase #7	$243.70	11.111%	$270.7775	$270.78	$270.80	$270.80
7 purchase totals =	$786.32		$841.0058	$841.01	$841.00	$841.10