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	$187.25	10.473%	$206.8607	$206.86	$206.85	$206.90
Purchase #2	$102.72	6.642%	$109.5427	$109.54	$109.55	$109.50
Purchase #3	$49.64	7.587%	$53.4062	$53.41	$53.40	$53.40
Purchase #4	$59.69	4.671%	$62.4781	$62.48	$62.50	$62.50
Purchase #5	$35.27	11.103%	$39.186	$39.19	$39.20	$39.20
Purchase #6	$44.78	6.709%	$47.7843	$47.78	$47.80	$47.80
Purchase #7	$205.73	6.824%	$219.769	$219.77	$219.75	$219.80
7 purchase totals =	$685.08		$739.0270	$739.03	$739.05	$739.10