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	$109.69	5.336%	$115.5431	$115.54	$115.55	$115.50
Purchase #2	$167.41	9.258%	$182.9088	$182.91	$182.90	$182.90
Purchase #3	$137.56	13.856%	$156.6203	$156.62	$156.60	$156.60
Purchase #4	$223.92	8.280%	$242.4606	$242.46	$242.45	$242.50
Purchase #5	$111.41	11.102%	$123.7787	$123.78	$123.80	$123.80
Purchase #6	$178.73	3.658%	$185.2679	$185.27	$185.25	$185.30
Purchase #7	$31.74	3.429%	$32.8284	$32.83	$32.85	$32.80
7 purchase totals =	$960.46		$1,039.4078	$1,039.41	$1,039.40	$1,039.40