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	$113.93	8.110%	$123.1697	$123.17	$123.15	$123.20
Purchase #2	$80.25	7.761%	$86.4782	$86.48	$86.50	$86.50
Purchase #3	$111.25	7.373%	$119.4525	$119.45	$119.45	$119.50
Purchase #4	$247.40	10.526%	$273.4413	$273.44	$273.45	$273.40
Purchase #5	$126.68	7.384%	$136.0341	$136.03	$136.05	$136.00
Purchase #6	$220.55	7.180%	$236.3855	$236.39	$236.40	$236.40
Purchase #7	$106.73	9.224%	$116.5748	$116.57	$116.55	$116.60
7 purchase totals =	$1,006.79		$1,091.5361	$1,091.53	$1,091.55	$1,091.60