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	$85.97	3.254%	$88.7675	$88.77	$88.75	$88.80
Purchase #2	$98.82	4.566%	$103.3321	$103.33	$103.35	$103.30
Purchase #3	$45.33	7.629%	$48.7882	$48.79	$48.80	$48.80
Purchase #4	$182.51	5.387%	$192.3418	$192.34	$192.35	$192.30
Purchase #5	$104.47	11.341%	$116.3179	$116.32	$116.30	$116.30
Purchase #6	$209.35	3.124%	$215.8901	$215.89	$215.90	$215.90
Purchase #7	$133.31	4.854%	$139.7809	$139.78	$139.80	$139.80
7 purchase totals =	$859.76		$905.2185	$905.22	$905.25	$905.20