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	$106.82	6.632%	$113.9043	$113.90	$113.90	$113.90
Purchase #2	$250.27	3.732%	$259.6101	$259.61	$259.60	$259.60
Purchase #3	$63.78	11.629%	$71.197	$71.20	$71.20	$71.20
Purchase #4	$219.32	9.812%	$240.8397	$240.84	$240.85	$240.80
Purchase #5	$72.91	3.400%	$75.3889	$75.39	$75.40	$75.40
Purchase #6	$135.49	4.657%	$141.7998	$141.80	$141.80	$141.80
Purchase #7	$81.41	11.232%	$90.554	$90.55	$90.55	$90.60
7 purchase totals =	$930.00		$993.2938	$993.29	$993.30	$993.30