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	$61.54	4.134%	$64.0841	$64.08	$64.10	$64.10
Purchase #2	$70.94	10.730%	$78.5519	$78.55	$78.55	$78.60
Purchase #3	$29.42	13.818%	$33.4853	$33.49	$33.50	$33.50
Purchase #4	$150.38	7.677%	$161.9247	$161.92	$161.90	$161.90
Purchase #5	$16.49	9.568%	$18.0678	$18.07	$18.05	$18.10
Purchase #6	$246.79	3.867%	$256.3334	$256.33	$256.35	$256.30
Purchase #7	$68.76	11.808%	$76.8792	$76.88	$76.90	$76.90
7 purchase totals =	$644.32		$689.3264	$689.32	$689.35	$689.40