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	$237.32	12.553%	$267.1108	$267.11	$267.10	$267.10
Purchase #2	$126.26	4.506%	$131.9493	$131.95	$131.95	$131.90
Purchase #3	$195.26	13.498%	$221.6162	$221.62	$221.60	$221.60
Purchase #4	$149.93	13.328%	$169.9127	$169.91	$169.90	$169.90
Purchase #5	$70.68	11.484%	$78.7969	$78.80	$78.80	$78.80
Purchase #6	$84.30	6.207%	$89.5325	$89.53	$89.55	$89.50
Purchase #7	$184.30	6.601%	$196.4656	$196.47	$196.45	$196.50
7 purchase totals =	$1,048.05		$1,155.3840	$1,155.39	$1,155.35	$1,155.30