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	$37.44	12.575%	$42.1481	$42.15	$42.15	$42.10
Purchase #2	$236.95	7.174%	$253.9488	$253.95	$253.95	$253.90
Purchase #3	$241.93	11.869%	$270.6447	$270.64	$270.65	$270.60
Purchase #4	$153.41	7.413%	$164.7823	$164.78	$164.80	$164.80
Purchase #5	$240.55	9.640%	$263.739	$263.74	$263.75	$263.70
Purchase #6	$101.94	3.414%	$105.4202	$105.42	$105.40	$105.40
Purchase #7	$179.42	11.396%	$199.8667	$199.87	$199.85	$199.90
7 purchase totals =	$1,191.64		$1,300.5498	$1,300.55	$1,300.55	$1,300.40