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	$170.87	6.644%	$182.2226	$182.22	$182.20	$182.20
Purchase #2	$168.38	10.231%	$185.607	$185.61	$185.60	$185.60
Purchase #3	$71.73	9.409%	$78.4791	$78.48	$78.50	$78.50
Purchase #4	$12.29	4.655%	$12.8621	$12.86	$12.85	$12.90
Purchase #5	$31.60	3.511%	$32.7095	$32.71	$32.70	$32.70
Purchase #6	$229.78	12.824%	$259.247	$259.25	$259.25	$259.20
Purchase #7	$157.42	7.430%	$169.1163	$169.12	$169.10	$169.10
7 purchase totals =	$842.07		$920.2436	$920.25	$920.20	$920.20