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	$171.39	6.659%	$182.8029	$182.80	$182.80	$182.80
Purchase #2	$226.69	7.415%	$243.4991	$243.50	$243.50	$243.50
Purchase #3	$91.25	13.590%	$103.6509	$103.65	$103.65	$103.70
Purchase #4	$91.96	11.246%	$102.3018	$102.30	$102.30	$102.30
Purchase #5	$207.79	3.570%	$215.2081	$215.21	$215.20	$215.20
Purchase #6	$45.35	4.829%	$47.54	$47.54	$47.55	$47.50
Purchase #7	$72.46	8.329%	$78.4952	$78.50	$78.50	$78.50
7 purchase totals =	$906.89		$973.4980	$973.50	$973.50	$973.50