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	$80.59	10.736%	$89.2421	$89.24	$89.25	$89.20
Purchase #2	$36.89	12.290%	$41.4238	$41.42	$41.40	$41.40
Purchase #3	$72.63	9.357%	$79.426	$79.43	$79.45	$79.40
Purchase #4	$116.40	11.214%	$129.4531	$129.45	$129.45	$129.50
Purchase #5	$213.60	5.196%	$224.6987	$224.70	$224.70	$224.70
Purchase #6	$108.84	11.680%	$121.5525	$121.55	$121.55	$121.60
Purchase #7	$88.56	11.196%	$98.4752	$98.48	$98.50	$98.50
7 purchase totals =	$717.51		$784.2714	$784.27	$784.30	$784.30