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	$220.89	12.449%	$248.3886	$248.39	$248.40	$248.40
Purchase #2	$111.52	11.726%	$124.5968	$124.60	$124.60	$124.60
Purchase #3	$238.42	13.474%	$270.5447	$270.54	$270.55	$270.50
Purchase #4	$139.73	7.741%	$150.5465	$150.55	$150.55	$150.50
Purchase #5	$116.32	10.549%	$128.5906	$128.59	$128.60	$128.60
Purchase #6	$28.56	10.603%	$31.5882	$31.59	$31.60	$31.60
Purchase #7	$196.42	13.566%	$223.0663	$223.07	$223.05	$223.10
7 purchase totals =	$1,051.86		$1,177.3217	$1,177.33	$1,177.35	$1,177.30