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	$138.59	8.803%	$150.7901	$150.79	$150.80	$150.80
Purchase #2	$221.71	9.794%	$243.4243	$243.42	$243.40	$243.40
Purchase #3	$76.96	12.781%	$86.7963	$86.80	$86.80	$86.80
Purchase #4	$170.71	5.184%	$179.5596	$179.56	$179.55	$179.60
Purchase #5	$69.85	12.232%	$78.3941	$78.39	$78.40	$78.40
Purchase #6	$210.27	4.103%	$218.8974	$218.90	$218.90	$218.90
Purchase #7	$67.28	5.469%	$70.9595	$70.96	$70.95	$71.00
7 purchase totals =	$955.37		$1,028.8213	$1,028.82	$1,028.80	$1,028.90