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	$109.31	9.407%	$119.5928	$119.59	$119.60	$119.60
Purchase #2	$83.70	7.508%	$89.9842	$89.98	$90.00	$90.00
Purchase #3	$152.27	4.815%	$159.6018	$159.60	$159.60	$159.60
Purchase #4	$94.66	10.826%	$104.9079	$104.91	$104.90	$104.90
Purchase #5	$168.38	12.394%	$189.249	$189.25	$189.25	$189.20
Purchase #6	$122.53	7.728%	$131.9991	$132.00	$132.00	$132.00
Purchase #7	$33.85	9.334%	$37.0096	$37.01	$37.00	$37.00
7 purchase totals =	$764.70		$832.3444	$832.34	$832.35	$832.30