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	$74.54	12.814%	$84.0916	$84.09	$84.10	$84.10
Purchase #2	$36.28	3.618%	$37.5926	$37.59	$37.60	$37.60
Purchase #3	$236.59	3.825%	$245.6396	$245.64	$245.65	$245.60
Purchase #4	$66.69	9.217%	$72.8368	$72.84	$72.85	$72.80
Purchase #5	$233.48	13.433%	$264.8434	$264.84	$264.85	$264.80
Purchase #6	$35.48	5.404%	$37.3973	$37.40	$37.40	$37.40
Purchase #7	$179.43	9.693%	$196.8221	$196.82	$196.80	$196.80
7 purchase totals =	$862.49		$939.2234	$939.22	$939.25	$939.10