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	$213.60	3.188%	$220.4096	$220.41	$220.40	$220.40
Purchase #2	$35.34	10.865%	$39.1797	$39.18	$39.20	$39.20
Purchase #3	$131.28	9.871%	$144.2386	$144.24	$144.25	$144.20
Purchase #4	$96.81	13.567%	$109.9442	$109.94	$109.95	$109.90
Purchase #5	$219.48	13.666%	$249.4741	$249.47	$249.45	$249.50
Purchase #6	$90.96	4.282%	$94.8549	$94.85	$94.85	$94.90
Purchase #7	$212.43	4.256%	$221.471	$221.47	$221.45	$221.50
7 purchase totals =	$999.90		$1,079.5721	$1,079.56	$1,079.55	$1,079.60