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	$37.54	13.446%	$42.5876	$42.59	$42.60	$42.60
Purchase #2	$87.46	11.254%	$97.3027	$97.30	$97.30	$97.30
Purchase #3	$203.29	13.710%	$231.1611	$231.16	$231.15	$231.20
Purchase #4	$68.56	7.181%	$73.4833	$73.48	$73.50	$73.50
Purchase #5	$13.94	4.341%	$14.5451	$14.55	$14.55	$14.50
Purchase #6	$187.82	11.801%	$209.9846	$209.98	$210.00	$210.00
Purchase #7	$227.29	4.671%	$237.9067	$237.91	$237.90	$237.90
7 purchase totals =	$825.90		$906.9711	$906.97	$907.00	$907.00