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	$167.81	13.392%	$190.2831	$190.28	$190.30	$190.30
Purchase #2	$109.50	7.621%	$117.845	$117.85	$117.85	$117.80
Purchase #3	$64.44	11.121%	$71.6064	$71.61	$71.60	$71.60
Purchase #4	$140.98	9.175%	$153.9149	$153.91	$153.90	$153.90
Purchase #5	$92.46	11.374%	$102.9764	$102.98	$103.00	$103.00
Purchase #6	$96.26	8.539%	$104.4796	$104.48	$104.50	$104.50
Purchase #7	$191.43	11.715%	$213.856	$213.86	$213.85	$213.90
7 purchase totals =	$862.88		$954.9614	$954.97	$955.00	$955.00