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	$109.79	3.424%	$113.5492	$113.55	$113.55	$113.50
Purchase #2	$188.29	11.135%	$209.2561	$209.26	$209.25	$209.30
Purchase #3	$109.35	6.425%	$116.3757	$116.38	$116.40	$116.40
Purchase #4	$13.33	13.536%	$15.1343	$15.13	$15.15	$15.10
Purchase #5	$142.89	5.696%	$151.029	$151.03	$151.05	$151.00
Purchase #6	$144.72	13.403%	$164.1168	$164.12	$164.10	$164.10
Purchase #7	$73.39	6.514%	$78.1706	$78.17	$78.15	$78.20
7 purchase totals =	$781.76		$847.6317	$847.64	$847.65	$847.60