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	$6.79	13.240%	$7.689	$7.69	$7.70	$7.70
Purchase #2	$196.71	5.197%	$206.933	$206.93	$206.95	$206.90
Purchase #3	$35.35	11.183%	$39.3032	$39.30	$39.30	$39.30
Purchase #4	$129.80	4.556%	$135.7137	$135.71	$135.70	$135.70
Purchase #5	$31.66	9.106%	$34.543	$34.54	$34.55	$34.50
Purchase #6	$173.86	4.740%	$182.101	$182.10	$182.10	$182.10
Purchase #7	$59.46	3.107%	$61.3074	$61.31	$61.30	$61.30
7 purchase totals =	$633.63		$667.5903	$667.58	$667.60	$667.50