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	$45.53	6.744%	$48.6005	$48.60	$48.60	$48.60
Purchase #2	$180.53	8.605%	$196.0646	$196.06	$196.05	$196.10
Purchase #3	$209.48	11.589%	$233.7566	$233.76	$233.75	$233.80
Purchase #4	$243.82	12.141%	$273.4222	$273.42	$273.40	$273.40
Purchase #5	$157.93	13.303%	$178.9394	$178.94	$178.95	$178.90
Purchase #6	$170.30	8.328%	$184.4826	$184.48	$184.50	$184.50
Purchase #7	$148.73	12.369%	$167.1264	$167.13	$167.15	$167.10
7 purchase totals =	$1,156.32		$1,282.3923	$1,282.39	$1,282.40	$1,282.40