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	$6.90	11.224%	$7.6745	$7.67	$7.65	$7.70
Purchase #2	$113.27	11.770%	$126.6019	$126.60	$126.60	$126.60
Purchase #3	$228.78	7.430%	$245.7784	$245.78	$245.80	$245.80
Purchase #4	$51.38	10.299%	$56.6716	$56.67	$56.65	$56.70
Purchase #5	$222.54	11.215%	$247.4979	$247.50	$247.50	$247.50
Purchase #6	$64.47	11.364%	$71.7964	$71.80	$71.80	$71.80
Purchase #7	$214.79	13.306%	$243.37	$243.37	$243.35	$243.40
7 purchase totals =	$902.13		$999.3907	$999.39	$999.35	$999.50