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	$19.64	7.436%	$21.1004	$21.10	$21.10	$21.10
Purchase #2	$176.80	11.374%	$196.9092	$196.91	$196.90	$196.90
Purchase #3	$197.89	7.865%	$213.454	$213.45	$213.45	$213.50
Purchase #4	$202.87	9.665%	$222.4774	$222.48	$222.50	$222.50
Purchase #5	$21.56	3.127%	$22.2342	$22.23	$22.25	$22.20
Purchase #6	$208.88	9.412%	$228.5398	$228.54	$228.55	$228.50
Purchase #7	$121.88	11.308%	$135.6622	$135.66	$135.65	$135.70
7 purchase totals =	$949.52		$1,040.3772	$1,040.37	$1,040.40	$1,040.40