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	$63.54	6.166%	$67.4579	$67.46	$67.45	$67.50
Purchase #2	$135.54	12.764%	$152.8403	$152.84	$152.85	$152.80
Purchase #3	$58.37	13.445%	$66.2178	$66.22	$66.20	$66.20
Purchase #4	$78.44	7.818%	$84.5724	$84.57	$84.55	$84.60
Purchase #5	$246.67	3.181%	$254.5166	$254.52	$254.50	$254.50
Purchase #6	$213.48	9.204%	$233.1287	$233.13	$233.15	$233.10
Purchase #7	$201.74	3.514%	$208.8291	$208.83	$208.85	$208.80
7 purchase totals =	$997.78		$1,067.5628	$1,067.57	$1,067.55	$1,067.50