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	$37.80	6.656%	$40.316	$40.32	$40.30	$40.30
Purchase #2	$101.62	7.822%	$109.5687	$109.57	$109.55	$109.60
Purchase #3	$120.79	10.252%	$133.1734	$133.17	$133.15	$133.20
Purchase #4	$47.32	6.795%	$50.5354	$50.54	$50.55	$50.50
Purchase #5	$121.69	8.385%	$131.8937	$131.89	$131.90	$131.90
Purchase #6	$82.39	10.611%	$91.1324	$91.13	$91.15	$91.10
Purchase #7	$12.81	12.550%	$14.4177	$14.42	$14.40	$14.40
7 purchase totals =	$524.42		$571.0373	$571.04	$571.00	$571.00