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	$131.77	3.302%	$136.121	$136.12	$136.10	$136.10
Purchase #2	$219.35	3.443%	$226.9022	$226.90	$226.90	$226.90
Purchase #3	$7.29	3.616%	$7.5536	$7.55	$7.55	$7.60
Purchase #4	$173.74	10.455%	$191.9045	$191.90	$191.90	$191.90
Purchase #5	$213.92	12.834%	$241.3745	$241.37	$241.35	$241.40
Purchase #6	$163.31	10.663%	$180.7237	$180.72	$180.70	$180.70
Purchase #7	$135.48	5.182%	$142.5006	$142.50	$142.50	$142.50
7 purchase totals =	$1,044.86		$1,127.0801	$1,127.06	$1,127.00	$1,127.10