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	$129.86	5.693%	$137.2529	$137.25	$137.25	$137.30
Purchase #2	$183.53	7.126%	$196.6083	$196.61	$196.60	$196.60
Purchase #3	$247.86	9.835%	$272.237	$272.24	$272.25	$272.20
Purchase #4	$165.89	13.682%	$188.5871	$188.59	$188.60	$188.60
Purchase #5	$221.91	3.250%	$229.1221	$229.12	$229.10	$229.10
Purchase #6	$211.58	8.504%	$229.5728	$229.57	$229.55	$229.60
Purchase #7	$76.73	6.253%	$81.5279	$81.53	$81.55	$81.50
7 purchase totals =	$1,237.36		$1,334.9081	$1,334.91	$1,334.90	$1,334.90