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	$102.25	4.200%	$106.5445	$106.54	$106.55	$106.50
Purchase #2	$128.87	10.438%	$142.3215	$142.32	$142.30	$142.30
Purchase #3	$167.60	4.645%	$175.385	$175.39	$175.40	$175.40
Purchase #4	$85.31	10.855%	$94.5704	$94.57	$94.55	$94.60
Purchase #5	$134.43	4.426%	$140.3799	$140.38	$140.40	$140.40
Purchase #6	$131.26	6.386%	$139.6423	$139.64	$139.65	$139.60
Purchase #7	$35.80	11.385%	$39.8758	$39.88	$39.90	$39.90
7 purchase totals =	$785.52		$838.7194	$838.72	$838.75	$838.70