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	$151.96	12.662%	$171.2012	$171.20	$171.20	$171.20
Purchase #2	$47.29	13.739%	$53.7872	$53.79	$53.80	$53.80
Purchase #3	$95.38	10.792%	$105.6734	$105.67	$105.65	$105.70
Purchase #4	$189.67	9.333%	$207.3719	$207.37	$207.35	$207.40
Purchase #5	$67.61	4.142%	$70.4104	$70.41	$70.40	$70.40
Purchase #6	$196.59	7.272%	$210.886	$210.89	$210.90	$210.90
Purchase #7	$27.54	8.498%	$29.8803	$29.88	$29.90	$29.90
7 purchase totals =	$776.04		$849.2104	$849.21	$849.20	$849.30