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	$142.36	4.610%	$148.9228	$148.92	$148.90	$148.90
Purchase #2	$45.73	12.267%	$51.3397	$51.34	$51.35	$51.30
Purchase #3	$84.60	10.566%	$93.5388	$93.54	$93.55	$93.50
Purchase #4	$175.93	11.853%	$196.783	$196.78	$196.80	$196.80
Purchase #5	$130.42	12.645%	$146.9116	$146.91	$146.90	$146.90
Purchase #6	$157.27	9.102%	$171.5847	$171.58	$171.60	$171.60
Purchase #7	$103.69	13.447%	$117.6332	$117.63	$117.65	$117.60
7 purchase totals =	$840.00		$926.7138	$926.70	$926.75	$926.60