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	$245.90	11.288%	$273.6572	$273.66	$273.65	$273.70
Purchase #2	$178.71	3.828%	$185.551	$185.55	$185.55	$185.60
Purchase #3	$49.65	12.667%	$55.9392	$55.94	$55.95	$55.90
Purchase #4	$250.33	9.171%	$273.2878	$273.29	$273.30	$273.30
Purchase #5	$152.98	13.662%	$173.8801	$173.88	$173.90	$173.90
Purchase #6	$86.57	9.270%	$94.595	$94.60	$94.60	$94.60
Purchase #7	$189.63	5.365%	$199.8036	$199.80	$199.80	$199.80
7 purchase totals =	$1,153.77		$1,256.7139	$1,256.72	$1,256.75	$1,256.80