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	$18.62	9.196%	$20.3323	$20.33	$20.35	$20.30
Purchase #2	$85.57	10.654%	$94.6866	$94.69	$94.70	$94.70
Purchase #3	$156.43	4.276%	$163.1189	$163.12	$163.10	$163.10
Purchase #4	$135.96	5.547%	$143.5017	$143.50	$143.50	$143.50
Purchase #5	$78.51	5.617%	$82.9199	$82.92	$82.90	$82.90
Purchase #6	$84.91	5.195%	$89.3211	$89.32	$89.30	$89.30
Purchase #7	$41.31	5.767%	$43.6923	$43.69	$43.70	$43.70
7 purchase totals =	$601.31		$637.5728	$637.57	$637.55	$637.50