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	$73.43	7.717%	$79.0966	$79.10	$79.10	$79.10
Purchase #2	$154.96	10.379%	$171.0433	$171.04	$171.05	$171.00
Purchase #3	$108.51	3.198%	$111.9801	$111.98	$112.00	$112.00
Purchase #4	$123.86	11.273%	$137.8227	$137.82	$137.80	$137.80
Purchase #5	$238.92	10.715%	$264.5203	$264.52	$264.50	$264.50
Purchase #6	$197.53	10.553%	$218.3753	$218.38	$218.40	$218.40
Purchase #7	$53.41	7.490%	$57.4104	$57.41	$57.40	$57.40
7 purchase totals =	$950.62		$1,040.2487	$1,040.25	$1,040.25	$1,040.20