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	$25.33	11.458%	$28.2323	$28.23	$28.25	$28.20
Purchase #2	$27.82	3.544%	$28.8059	$28.81	$28.80	$28.80
Purchase #3	$159.82	13.472%	$181.351	$181.35	$181.35	$181.40
Purchase #4	$209.94	5.353%	$221.1781	$221.18	$221.20	$221.20
Purchase #5	$82.29	4.349%	$85.8688	$85.87	$85.85	$85.90
Purchase #6	$151.85	13.859%	$172.8949	$172.89	$172.90	$172.90
Purchase #7	$42.44	10.379%	$46.8448	$46.84	$46.85	$46.80
7 purchase totals =	$699.49		$765.1758	$765.17	$765.20	$765.20