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	$77.54	3.716%	$80.4214	$80.42	$80.40	$80.40
Purchase #2	$13.77	12.401%	$15.4776	$15.48	$15.50	$15.50
Purchase #3	$226.75	7.330%	$243.3708	$243.37	$243.35	$243.40
Purchase #4	$84.82	6.352%	$90.2078	$90.21	$90.20	$90.20
Purchase #5	$80.36	6.848%	$85.8631	$85.86	$85.85	$85.90
Purchase #6	$136.34	13.185%	$154.3164	$154.32	$154.30	$154.30
Purchase #7	$221.46	10.138%	$243.9116	$243.91	$243.90	$243.90
7 purchase totals =	$841.04		$913.5687	$913.57	$913.50	$913.60