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	$31.80	12.574%	$35.7985	$35.80	$35.80	$35.80
Purchase #2	$156.48	8.426%	$169.665	$169.67	$169.65	$169.70
Purchase #3	$223.86	9.618%	$245.3909	$245.39	$245.40	$245.40
Purchase #4	$90.47	10.472%	$99.944	$99.94	$99.95	$99.90
Purchase #5	$141.77	10.653%	$156.8728	$156.87	$156.85	$156.90
Purchase #6	$201.67	7.246%	$216.283	$216.28	$216.30	$216.30
Purchase #7	$51.28	10.238%	$56.53	$56.53	$56.55	$56.50
7 purchase totals =	$897.33		$980.4842	$980.48	$980.50	$980.50