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	$73.79	6.251%	$78.4026	$78.40	$78.40	$78.40
Purchase #2	$64.92	5.535%	$68.5133	$68.51	$68.50	$68.50
Purchase #3	$94.27	6.459%	$100.3589	$100.36	$100.35	$100.40
Purchase #4	$213.61	10.691%	$236.447	$236.45	$236.45	$236.40
Purchase #5	$108.89	3.822%	$113.0518	$113.05	$113.05	$113.10
Purchase #6	$64.75	4.789%	$67.8509	$67.85	$67.85	$67.90
Purchase #7	$67.74	4.395%	$70.7172	$70.72	$70.70	$70.70
7 purchase totals =	$687.97		$735.3417	$735.34	$735.30	$735.40