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	$205.57	8.534%	$223.1133	$223.11	$223.10	$223.10
Purchase #2	$60.29	9.145%	$65.8035	$65.80	$65.80	$65.80
Purchase #3	$61.79	8.478%	$67.0286	$67.03	$67.05	$67.00
Purchase #4	$215.80	3.676%	$223.7328	$223.73	$223.75	$223.70
Purchase #5	$54.82	3.290%	$56.6236	$56.62	$56.60	$56.60
Purchase #6	$85.29	7.154%	$91.3916	$91.39	$91.40	$91.40
Purchase #7	$83.93	7.666%	$90.3641	$90.36	$90.35	$90.40
7 purchase totals =	$767.49		$818.0575	$818.04	$818.05	$818.00