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	$56.42	5.443%	$59.4909	$59.49	$59.50	$59.50
Purchase #2	$170.40	9.371%	$186.3682	$186.37	$186.35	$186.40
Purchase #3	$234.89	4.445%	$245.3309	$245.33	$245.35	$245.30
Purchase #4	$226.97	6.508%	$241.7412	$241.74	$241.75	$241.70
Purchase #5	$135.89	3.801%	$141.0552	$141.06	$141.05	$141.10
Purchase #6	$216.26	5.166%	$227.432	$227.43	$227.45	$227.40
Purchase #7	$166.50	12.221%	$186.848	$186.85	$186.85	$186.80
7 purchase totals =	$1,207.33		$1,288.2664	$1,288.27	$1,288.30	$1,288.20