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	$53.41	11.362%	$59.4784	$59.48	$59.50	$59.50
Purchase #2	$148.44	13.553%	$168.5581	$168.56	$168.55	$168.60
Purchase #3	$102.34	9.822%	$112.3918	$112.39	$112.40	$112.40
Purchase #4	$156.74	6.271%	$166.5692	$166.57	$166.55	$166.60
Purchase #5	$18.94	12.352%	$21.2795	$21.28	$21.30	$21.30
Purchase #6	$203.89	13.300%	$231.0074	$231.01	$231.00	$231.00
Purchase #7	$179.73	7.401%	$193.0318	$193.03	$193.05	$193.00
7 purchase totals =	$863.49		$952.3162	$952.32	$952.35	$952.40