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	$25.98	5.210%	$27.3336	$27.33	$27.35	$27.30
Purchase #2	$68.65	3.574%	$71.1036	$71.10	$71.10	$71.10
Purchase #3	$63.85	12.624%	$71.9104	$71.91	$71.90	$71.90
Purchase #4	$238.50	5.109%	$250.685	$250.69	$250.70	$250.70
Purchase #5	$194.54	7.338%	$208.8153	$208.82	$208.80	$208.80
Purchase #6	$205.46	4.694%	$215.1043	$215.10	$215.10	$215.10
Purchase #7	$56.97	7.515%	$61.2513	$61.25	$61.25	$61.30
7 purchase totals =	$853.95		$906.2035	$906.20	$906.20	$906.20