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	$53.33	13.558%	$60.5605	$60.56	$60.55	$60.60
Purchase #2	$82.56	8.858%	$89.8732	$89.87	$89.85	$89.90
Purchase #3	$52.89	12.658%	$59.5848	$59.58	$59.60	$59.60
Purchase #4	$187.40	9.806%	$205.7764	$205.78	$205.80	$205.80
Purchase #5	$236.75	7.258%	$253.9333	$253.93	$253.95	$253.90
Purchase #6	$53.86	11.199%	$59.8918	$59.89	$59.90	$59.90
Purchase #7	$162.54	12.443%	$182.7649	$182.76	$182.75	$182.80
7 purchase totals =	$829.33		$912.3849	$912.37	$912.40	$912.50