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	$70.85	6.308%	$75.3192	$75.32	$75.30	$75.30
Purchase #2	$211.88	12.527%	$238.4222	$238.42	$238.40	$238.40
Purchase #3	$206.45	3.631%	$213.9462	$213.95	$213.95	$213.90
Purchase #4	$144.50	12.614%	$162.7272	$162.73	$162.75	$162.70
Purchase #5	$156.47	7.481%	$168.1755	$168.18	$168.20	$168.20
Purchase #6	$92.65	11.470%	$103.277	$103.28	$103.30	$103.30
Purchase #7	$102.47	10.804%	$113.5409	$113.54	$113.55	$113.50
7 purchase totals =	$985.27		$1,075.4082	$1,075.42	$1,075.45	$1,075.30