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	$169.88	6.772%	$181.3843	$181.38	$181.40	$181.40
Purchase #2	$77.77	7.802%	$83.8376	$83.84	$83.85	$83.80
Purchase #3	$238.64	4.555%	$249.5101	$249.51	$249.50	$249.50
Purchase #4	$161.33	3.512%	$166.9959	$167.00	$167.00	$167.00
Purchase #5	$25.51	11.168%	$28.359	$28.36	$28.35	$28.40
Purchase #6	$86.96	4.442%	$90.8228	$90.82	$90.80	$90.80
Purchase #7	$229.41	3.516%	$237.4761	$237.48	$237.50	$237.50
7 purchase totals =	$989.50		$1,038.3858	$1,038.39	$1,038.40	$1,038.40