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	$68.46	5.391%	$72.1507	$72.15	$72.15	$72.20
Purchase #2	$217.84	13.630%	$247.5316	$247.53	$247.55	$247.50
Purchase #3	$100.40	7.124%	$107.5525	$107.55	$107.55	$107.60
Purchase #4	$117.93	5.526%	$124.4468	$124.45	$124.45	$124.40
Purchase #5	$80.96	10.347%	$89.3369	$89.34	$89.35	$89.30
Purchase #6	$5.69	13.377%	$6.4512	$6.45	$6.45	$6.50
Purchase #7	$20.66	6.206%	$21.9422	$21.94	$21.95	$21.90
7 purchase totals =	$611.94		$669.4119	$669.41	$669.45	$669.40