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	$43.89	8.341%	$47.5509	$47.55	$47.55	$47.60
Purchase #2	$113.81	10.213%	$125.4334	$125.43	$125.45	$125.40
Purchase #3	$34.76	7.372%	$37.3225	$37.32	$37.30	$37.30
Purchase #4	$103.79	5.295%	$109.2857	$109.29	$109.30	$109.30
Purchase #5	$79.48	4.830%	$83.3189	$83.32	$83.30	$83.30
Purchase #6	$150.43	13.860%	$171.2796	$171.28	$171.30	$171.30
Purchase #7	$160.63	10.449%	$177.4142	$177.41	$177.40	$177.40
7 purchase totals =	$686.79		$751.6052	$751.60	$751.60	$751.60