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	$184.40	13.828%	$209.8988	$209.90	$209.90	$209.90
Purchase #2	$154.97	13.253%	$175.5082	$175.51	$175.50	$175.50
Purchase #3	$109.75	4.306%	$114.4758	$114.48	$114.50	$114.50
Purchase #4	$110.89	12.640%	$124.9065	$124.91	$124.90	$124.90
Purchase #5	$84.25	6.346%	$89.5965	$89.60	$89.60	$89.60
Purchase #6	$30.45	4.845%	$31.9253	$31.93	$31.95	$31.90
Purchase #7	$164.72	6.685%	$175.7315	$175.73	$175.75	$175.70
7 purchase totals =	$839.43		$922.0426	$922.06	$922.10	$922.00