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	$212.89	3.344%	$220.009	$220.01	$220.00	$220.00
Purchase #2	$173.38	13.156%	$196.1899	$196.19	$196.20	$196.20
Purchase #3	$28.68	10.844%	$31.7901	$31.79	$31.80	$31.80
Purchase #4	$168.85	11.254%	$187.8524	$187.85	$187.85	$187.90
Purchase #5	$82.36	11.147%	$91.5407	$91.54	$91.55	$91.50
Purchase #6	$38.36	9.248%	$41.9075	$41.91	$41.90	$41.90
Purchase #7	$76.89	6.846%	$82.1539	$82.15	$82.15	$82.20
7 purchase totals =	$781.41		$851.4435	$851.44	$851.45	$851.50