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	$84.25	7.206%	$90.3211	$90.32	$90.30	$90.30
Purchase #2	$143.64	13.376%	$162.8533	$162.85	$162.85	$162.90
Purchase #3	$222.59	10.661%	$246.3203	$246.32	$246.30	$246.30
Purchase #4	$86.30	11.369%	$96.1114	$96.11	$96.10	$96.10
Purchase #5	$167.87	7.305%	$180.1329	$180.13	$180.15	$180.10
Purchase #6	$156.76	12.263%	$175.9835	$175.98	$176.00	$176.00
Purchase #7	$228.48	13.776%	$259.9554	$259.96	$259.95	$260.00
7 purchase totals =	$1,089.89		$1,211.6779	$1,211.67	$1,211.65	$1,211.70