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	$33.71	11.549%	$37.6032	$37.60	$37.60	$37.60
Purchase #2	$62.41	13.484%	$70.8254	$70.83	$70.85	$70.80
Purchase #3	$173.71	5.293%	$182.9045	$182.90	$182.90	$182.90
Purchase #4	$9.79	7.458%	$10.5201	$10.52	$10.50	$10.50
Purchase #5	$89.68	7.397%	$96.3136	$96.31	$96.30	$96.30
Purchase #6	$174.90	13.424%	$198.3786	$198.38	$198.40	$198.40
Purchase #7	$132.64	8.441%	$143.8361	$143.84	$143.85	$143.80
7 purchase totals =	$676.84		$740.3815	$740.38	$740.40	$740.30