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	$86.48	12.849%	$97.5918	$97.59	$97.60	$97.60
Purchase #2	$167.94	13.272%	$190.229	$190.23	$190.25	$190.20
Purchase #3	$45.97	13.789%	$52.3088	$52.31	$52.30	$52.30
Purchase #4	$225.42	7.477%	$242.2747	$242.27	$242.25	$242.30
Purchase #5	$209.82	4.860%	$220.0173	$220.02	$220.00	$220.00
Purchase #6	$69.87	12.476%	$78.587	$78.59	$78.60	$78.60
Purchase #7	$73.79	4.232%	$76.9128	$76.91	$76.90	$76.90
7 purchase totals =	$879.29		$957.9214	$957.92	$957.90	$957.90