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	$132.33	5.399%	$139.4745	$139.47	$139.45	$139.50
Purchase #2	$209.56	7.605%	$225.497	$225.50	$225.50	$225.50
Purchase #3	$144.80	5.493%	$152.7539	$152.75	$152.75	$152.80
Purchase #4	$109.38	13.209%	$123.828	$123.83	$123.85	$123.80
Purchase #5	$110.81	8.674%	$120.4217	$120.42	$120.40	$120.40
Purchase #6	$63.30	13.767%	$72.0145	$72.01	$72.00	$72.00
Purchase #7	$82.63	7.664%	$88.9628	$88.96	$88.95	$89.00
7 purchase totals =	$852.81		$922.9524	$922.94	$922.90	$923.00