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	$36.79	11.217%	$40.9167	$40.92	$40.90	$40.90
Purchase #2	$198.27	9.250%	$216.61	$216.61	$216.60	$216.60
Purchase #3	$17.48	5.330%	$18.4117	$18.41	$18.40	$18.40
Purchase #4	$174.43	5.357%	$183.7742	$183.77	$183.75	$183.80
Purchase #5	$86.90	3.649%	$90.071	$90.07	$90.05	$90.10
Purchase #6	$134.88	4.764%	$141.3057	$141.31	$141.30	$141.30
Purchase #7	$41.68	7.320%	$44.731	$44.73	$44.75	$44.70
7 purchase totals =	$690.43		$735.8203	$735.82	$735.75	$735.80