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	$227.51	5.721%	$240.5258	$240.53	$240.55	$240.50
Purchase #2	$148.68	13.372%	$168.5615	$168.56	$168.55	$168.60
Purchase #3	$72.26	9.603%	$79.1991	$79.20	$79.20	$79.20
Purchase #4	$99.86	12.306%	$112.1488	$112.15	$112.15	$112.10
Purchase #5	$87.51	13.739%	$99.533	$99.53	$99.55	$99.50
Purchase #6	$78.48	3.291%	$81.0628	$81.06	$81.05	$81.10
Purchase #7	$129.40	9.370%	$141.5248	$141.52	$141.50	$141.50
7 purchase totals =	$843.70		$922.5558	$922.55	$922.55	$922.50