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	$19.33	6.557%	$20.5975	$20.60	$20.60	$20.60
Purchase #2	$94.82	12.361%	$106.5407	$106.54	$106.55	$106.50
Purchase #3	$187.56	6.260%	$199.3013	$199.30	$199.30	$199.30
Purchase #4	$153.69	9.179%	$167.7972	$167.80	$167.80	$167.80
Purchase #5	$6.38	7.445%	$6.855	$6.86	$6.85	$6.90
Purchase #6	$150.71	4.420%	$157.3714	$157.37	$157.35	$157.40
Purchase #7	$84.95	5.860%	$89.9281	$89.93	$89.95	$89.90
7 purchase totals =	$697.44		$748.3912	$748.40	$748.40	$748.40