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	$248.45	8.799%	$270.3111	$270.31	$270.30	$270.30
Purchase #2	$91.61	13.800%	$104.2522	$104.25	$104.25	$104.30
Purchase #3	$124.93	10.112%	$137.5629	$137.56	$137.55	$137.60
Purchase #4	$98.28	13.143%	$111.1969	$111.20	$111.20	$111.20
Purchase #5	$200.46	8.644%	$217.7878	$217.79	$217.80	$217.80
Purchase #6	$156.55	13.147%	$177.1316	$177.13	$177.15	$177.10
Purchase #7	$83.88	9.127%	$91.5357	$91.54	$91.55	$91.50
7 purchase totals =	$1,004.16		$1,109.7782	$1,109.78	$1,109.80	$1,109.80