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	$162.83	6.176%	$172.8864	$172.89	$172.90	$172.90
Purchase #2	$171.90	8.662%	$186.79	$186.79	$186.80	$186.80
Purchase #3	$54.50	12.855%	$61.506	$61.51	$61.50	$61.50
Purchase #4	$248.33	9.108%	$270.9479	$270.95	$270.95	$270.90
Purchase #5	$73.38	8.161%	$79.3685	$79.37	$79.35	$79.40
Purchase #6	$36.63	3.196%	$37.8007	$37.80	$37.80	$37.80
Purchase #7	$78.77	8.574%	$85.5237	$85.52	$85.50	$85.50
7 purchase totals =	$826.34		$894.8232	$894.83	$894.80	$894.80