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	$34.64	7.180%	$37.1272	$37.13	$37.15	$37.10
Purchase #2	$110.82	9.673%	$121.5396	$121.54	$121.55	$121.50
Purchase #3	$150.80	5.863%	$159.6414	$159.64	$159.65	$159.60
Purchase #4	$55.26	9.180%	$60.3329	$60.33	$60.35	$60.30
Purchase #5	$250.46	5.584%	$264.4457	$264.45	$264.45	$264.40
Purchase #6	$127.95	3.359%	$132.2478	$132.25	$132.25	$132.20
Purchase #7	$99.48	4.423%	$103.88	$103.88	$103.90	$103.90
7 purchase totals =	$829.41		$879.2146	$879.22	$879.30	$879.00