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	$231.87	12.266%	$260.3112	$260.31	$260.30	$260.30
Purchase #2	$93.84	5.275%	$98.7901	$98.79	$98.80	$98.80
Purchase #3	$104.44	7.106%	$111.8615	$111.86	$111.85	$111.90
Purchase #4	$156.76	12.765%	$176.7704	$176.77	$176.75	$176.80
Purchase #5	$104.34	8.524%	$113.2339	$113.23	$113.25	$113.20
Purchase #6	$57.76	6.433%	$61.4757	$61.48	$61.50	$61.50
Purchase #7	$166.88	8.790%	$181.5488	$181.55	$181.55	$181.50
7 purchase totals =	$915.89		$1,003.9916	$1,003.99	$1,004.00	$1,004.00