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	$176.78	3.298%	$182.6102	$182.61	$182.60	$182.60
Purchase #2	$70.57	11.488%	$78.6771	$78.68	$78.70	$78.70
Purchase #3	$205.95	7.121%	$220.6157	$220.62	$220.60	$220.60
Purchase #4	$29.60	12.334%	$33.2509	$33.25	$33.25	$33.30
Purchase #5	$128.28	13.270%	$145.3028	$145.30	$145.30	$145.30
Purchase #6	$37.62	12.569%	$42.3485	$42.35	$42.35	$42.30
Purchase #7	$205.68	7.489%	$221.0834	$221.08	$221.10	$221.10
7 purchase totals =	$854.48		$923.8886	$923.89	$923.90	$923.90