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	$152.87	7.461%	$164.2756	$164.28	$164.30	$164.30
Purchase #2	$149.92	12.624%	$168.8459	$168.85	$168.85	$168.80
Purchase #3	$184.59	13.661%	$209.8068	$209.81	$209.80	$209.80
Purchase #4	$43.61	6.697%	$46.5306	$46.53	$46.55	$46.50
Purchase #5	$164.54	3.288%	$169.9501	$169.95	$169.95	$170.00
Purchase #6	$76.26	3.155%	$78.666	$78.67	$78.65	$78.70
Purchase #7	$18.67	8.227%	$20.206	$20.21	$20.20	$20.20
7 purchase totals =	$790.46		$858.2810	$858.30	$858.30	$858.30