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	$75.74	3.484%	$78.3788	$78.38	$78.40	$78.40
Purchase #2	$18.48	8.772%	$20.1011	$20.10	$20.10	$20.10
Purchase #3	$248.27	9.565%	$272.017	$272.02	$272.00	$272.00
Purchase #4	$180.68	6.765%	$192.903	$192.90	$192.90	$192.90
Purchase #5	$219.28	3.677%	$227.3429	$227.34	$227.35	$227.30
Purchase #6	$176.34	8.594%	$191.4947	$191.49	$191.50	$191.50
Purchase #7	$57.90	5.831%	$61.2761	$61.28	$61.30	$61.30
7 purchase totals =	$976.69		$1,043.5136	$1,043.51	$1,043.55	$1,043.50