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	$123.90	6.433%	$131.8705	$131.87	$131.85	$131.90
Purchase #2	$229.25	11.532%	$255.6871	$255.69	$255.70	$255.70
Purchase #3	$170.90	10.279%	$188.4668	$188.47	$188.45	$188.50
Purchase #4	$206.48	6.571%	$220.0478	$220.05	$220.05	$220.00
Purchase #5	$23.56	13.772%	$26.8047	$26.80	$26.80	$26.80
Purchase #6	$213.75	4.196%	$222.719	$222.72	$222.70	$222.70
Purchase #7	$196.94	13.355%	$223.2413	$223.24	$223.25	$223.20
7 purchase totals =	$1,164.78		$1,268.8372	$1,268.84	$1,268.80	$1,268.80