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	$83.66	7.601%	$90.019	$90.02	$90.00	$90.00
Purchase #2	$151.37	11.293%	$168.4642	$168.46	$168.45	$168.50
Purchase #3	$120.39	3.309%	$124.3737	$124.37	$124.35	$124.40
Purchase #4	$156.80	3.803%	$162.7631	$162.76	$162.75	$162.80
Purchase #5	$153.74	9.739%	$168.7127	$168.71	$168.70	$168.70
Purchase #6	$186.63	12.735%	$210.3973	$210.40	$210.40	$210.40
Purchase #7	$249.78	13.830%	$284.3246	$284.32	$284.30	$284.30
7 purchase totals =	$1,102.37		$1,209.0546	$1,209.04	$1,208.95	$1,209.10