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	$64.40	10.482%	$71.1504	$71.15	$71.15	$71.20
Purchase #2	$242.68	9.351%	$265.373	$265.37	$265.35	$265.40
Purchase #3	$35.82	12.786%	$40.3999	$40.40	$40.40	$40.40
Purchase #4	$116.36	13.120%	$131.6264	$131.63	$131.65	$131.60
Purchase #5	$66.33	11.387%	$73.883	$73.88	$73.90	$73.90
Purchase #6	$93.41	6.828%	$99.788	$99.79	$99.80	$99.80
Purchase #7	$160.60	8.447%	$174.1659	$174.17	$174.15	$174.20
7 purchase totals =	$779.60		$856.3866	$856.39	$856.40	$856.50