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	$196.29	13.256%	$222.3102	$222.31	$222.30	$222.30
Purchase #2	$60.43	9.421%	$66.1231	$66.12	$66.10	$66.10
Purchase #3	$213.35	7.357%	$229.0462	$229.05	$229.05	$229.00
Purchase #4	$131.96	12.103%	$147.9311	$147.93	$147.95	$147.90
Purchase #5	$80.48	12.832%	$90.8072	$90.81	$90.80	$90.80
Purchase #6	$172.87	9.421%	$189.1561	$189.16	$189.15	$189.20
Purchase #7	$96.82	3.238%	$99.955	$99.96	$99.95	$100.00
7 purchase totals =	$952.20		$1,045.3289	$1,045.34	$1,045.30	$1,045.30