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	$30.86	4.626%	$32.2876	$32.29	$32.30	$32.30
Purchase #2	$234.35	7.345%	$251.563	$251.56	$251.55	$251.60
Purchase #3	$242.60	3.423%	$250.9042	$250.90	$250.90	$250.90
Purchase #4	$161.96	6.546%	$172.5619	$172.56	$172.55	$172.60
Purchase #5	$235.60	13.611%	$267.6675	$267.67	$267.65	$267.70
Purchase #6	$144.32	8.421%	$156.4732	$156.47	$156.45	$156.50
Purchase #7	$200.54	4.385%	$209.3337	$209.33	$209.35	$209.30
7 purchase totals =	$1,250.23		$1,340.7911	$1,340.78	$1,340.75	$1,340.90