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	$102.34	12.170%	$114.7948	$114.79	$114.80	$114.80
Purchase #2	$69.51	5.588%	$73.3942	$73.39	$73.40	$73.40
Purchase #3	$196.80	13.221%	$222.8189	$222.82	$222.80	$222.80
Purchase #4	$144.47	12.697%	$162.8134	$162.81	$162.80	$162.80
Purchase #5	$36.36	5.607%	$38.3987	$38.40	$38.40	$38.40
Purchase #6	$152.34	13.278%	$172.5677	$172.57	$172.55	$172.60
Purchase #7	$196.62	11.596%	$219.4201	$219.42	$219.40	$219.40
7 purchase totals =	$898.44		$1,004.2078	$1,004.20	$1,004.15	$1,004.20