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	$96.72	11.582%	$107.9221	$107.92	$107.90	$107.90
Purchase #2	$165.83	11.420%	$184.7678	$184.77	$184.75	$184.80
Purchase #3	$75.89	13.741%	$86.318	$86.32	$86.30	$86.30
Purchase #4	$72.94	9.523%	$79.8861	$79.89	$79.90	$79.90
Purchase #5	$76.55	7.310%	$82.1458	$82.15	$82.15	$82.10
Purchase #6	$92.98	11.347%	$103.5304	$103.53	$103.55	$103.50
Purchase #7	$134.48	4.546%	$140.5935	$140.59	$140.60	$140.60
7 purchase totals =	$715.39		$785.1637	$785.17	$785.15	$785.10