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	$90.59	12.869%	$102.248	$102.25	$102.25	$102.20
Purchase #2	$113.93	8.170%	$123.2381	$123.24	$123.25	$123.20
Purchase #3	$150.73	11.200%	$167.6118	$167.61	$167.60	$167.60
Purchase #4	$92.73	6.656%	$98.9021	$98.90	$98.90	$98.90
Purchase #5	$76.55	12.279%	$85.9496	$85.95	$85.95	$85.90
Purchase #6	$75.31	12.117%	$84.4353	$84.44	$84.45	$84.40
Purchase #7	$76.91	8.342%	$83.3258	$83.33	$83.35	$83.30
7 purchase totals =	$676.75		$745.7107	$745.72	$745.75	$745.50