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	$76.94	7.591%	$82.7805	$82.78	$82.80	$82.80
Purchase #2	$207.82	5.648%	$219.5577	$219.56	$219.55	$219.60
Purchase #3	$136.30	10.138%	$150.1181	$150.12	$150.10	$150.10
Purchase #4	$159.91	5.355%	$168.4732	$168.47	$168.45	$168.50
Purchase #5	$8.47	4.337%	$8.8373	$8.84	$8.85	$8.80
Purchase #6	$203.77	11.850%	$227.9167	$227.92	$227.90	$227.90
Purchase #7	$168.43	8.136%	$182.1335	$182.13	$182.15	$182.10
7 purchase totals =	$961.64		$1,039.8170	$1,039.82	$1,039.80	$1,039.80