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	$212.78	10.557%	$235.2432	$235.24	$235.25	$235.20
Purchase #2	$246.25	11.778%	$275.2533	$275.25	$275.25	$275.30
Purchase #3	$26.61	12.544%	$29.948	$29.95	$29.95	$29.90
Purchase #4	$180.40	5.450%	$190.2318	$190.23	$190.25	$190.20
Purchase #5	$113.33	9.342%	$123.9173	$123.92	$123.90	$123.90
Purchase #6	$166.56	12.260%	$186.9803	$186.98	$187.00	$187.00
Purchase #7	$250.66	11.833%	$280.3206	$280.32	$280.30	$280.30
7 purchase totals =	$1,196.59		$1,321.8945	$1,321.89	$1,321.90	$1,321.80