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	$198.74	12.511%	$223.6044	$223.60	$223.60	$223.60
Purchase #2	$103.80	10.731%	$114.9388	$114.94	$114.95	$114.90
Purchase #3	$227.70	13.112%	$257.556	$257.56	$257.55	$257.60
Purchase #4	$33.76	8.317%	$36.5678	$36.57	$36.55	$36.60
Purchase #5	$6.81	6.602%	$7.2596	$7.26	$7.25	$7.30
Purchase #6	$87.56	3.164%	$90.3304	$90.33	$90.35	$90.30
Purchase #7	$207.43	4.289%	$216.3267	$216.33	$216.35	$216.30
7 purchase totals =	$865.80		$946.5837	$946.59	$946.60	$946.60