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	$19.55	10.653%	$21.6327	$21.63	$21.65	$21.60
Purchase #2	$119.59	9.452%	$130.8936	$130.89	$130.90	$130.90
Purchase #3	$55.89	10.718%	$61.8803	$61.88	$61.90	$61.90
Purchase #4	$78.73	9.521%	$86.2259	$86.23	$86.25	$86.20
Purchase #5	$180.64	13.838%	$205.637	$205.64	$205.65	$205.60
Purchase #6	$155.44	8.592%	$168.7954	$168.80	$168.80	$168.80
Purchase #7	$151.35	12.508%	$170.2809	$170.28	$170.30	$170.30
7 purchase totals =	$761.19		$845.3458	$845.35	$845.45	$845.30