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	$38.36	6.667%	$40.9175	$40.92	$40.90	$40.90
Purchase #2	$167.27	12.731%	$188.5651	$188.57	$188.55	$188.60
Purchase #3	$246.29	7.402%	$264.5204	$264.52	$264.50	$264.50
Purchase #4	$248.30	13.630%	$282.1433	$282.14	$282.15	$282.10
Purchase #5	$225.60	7.104%	$241.6266	$241.63	$241.65	$241.60
Purchase #6	$196.71	13.852%	$223.9583	$223.96	$223.95	$224.00
Purchase #7	$63.97	5.838%	$67.7046	$67.70	$67.70	$67.70
7 purchase totals =	$1,186.50		$1,309.4358	$1,309.44	$1,309.40	$1,309.40