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	$37.83	12.519%	$42.5659	$42.57	$42.55	$42.60
Purchase #2	$166.85	12.176%	$187.1657	$187.17	$187.15	$187.20
Purchase #3	$90.25	6.662%	$96.2625	$96.26	$96.25	$96.30
Purchase #4	$119.88	5.370%	$126.3176	$126.32	$126.30	$126.30
Purchase #5	$43.67	6.347%	$46.4417	$46.44	$46.45	$46.40
Purchase #6	$248.67	12.743%	$280.358	$280.36	$280.35	$280.40
Purchase #7	$92.29	3.833%	$95.8275	$95.83	$95.85	$95.80
7 purchase totals =	$799.44		$874.9389	$874.95	$874.90	$875.00