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	$190.78	13.696%	$216.9092	$216.91	$216.90	$216.90
Purchase #2	$76.34	10.241%	$84.158	$84.16	$84.15	$84.20
Purchase #3	$193.26	12.403%	$217.23	$217.23	$217.25	$217.20
Purchase #4	$215.97	8.520%	$234.3706	$234.37	$234.35	$234.40
Purchase #5	$198.58	13.472%	$225.3327	$225.33	$225.35	$225.30
Purchase #6	$80.32	10.839%	$89.0259	$89.03	$89.05	$89.00
Purchase #7	$218.62	6.687%	$233.2391	$233.24	$233.25	$233.20
7 purchase totals =	$1,173.87		$1,300.2655	$1,300.27	$1,300.30	$1,300.20