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	$121.42	8.113%	$131.2708	$131.27	$131.25	$131.30
Purchase #2	$181.42	4.487%	$189.5603	$189.56	$189.55	$189.60
Purchase #3	$240.82	12.215%	$270.2362	$270.24	$270.25	$270.20
Purchase #4	$79.74	3.556%	$82.5756	$82.58	$82.60	$82.60
Purchase #5	$93.31	3.378%	$96.462	$96.46	$96.45	$96.50
Purchase #6	$29.90	9.557%	$32.7575	$32.76	$32.75	$32.80
Purchase #7	$170.88	9.221%	$186.6368	$186.64	$186.65	$186.60
7 purchase totals =	$917.49		$989.4992	$989.51	$989.50	$989.60