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	$163.87	13.658%	$186.2514	$186.25	$186.25	$186.30
Purchase #2	$156.55	3.447%	$161.9463	$161.95	$161.95	$161.90
Purchase #3	$131.72	7.329%	$141.3738	$141.37	$141.35	$141.40
Purchase #4	$38.31	10.521%	$42.3406	$42.34	$42.35	$42.30
Purchase #5	$203.36	10.282%	$224.2695	$224.27	$224.25	$224.30
Purchase #6	$18.56	3.697%	$19.2462	$19.25	$19.25	$19.20
Purchase #7	$60.86	8.278%	$65.898	$65.90	$65.90	$65.90
7 purchase totals =	$773.23		$841.3258	$841.33	$841.30	$841.30