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	$136.78	12.809%	$154.3002	$154.30	$154.30	$154.30
Purchase #2	$241.71	5.636%	$255.3328	$255.33	$255.35	$255.30
Purchase #3	$72.25	9.224%	$78.9143	$78.91	$78.90	$78.90
Purchase #4	$85.33	7.397%	$91.6419	$91.64	$91.65	$91.60
Purchase #5	$237.34	12.257%	$266.4308	$266.43	$266.45	$266.40
Purchase #6	$29.80	8.604%	$32.364	$32.36	$32.35	$32.40
Purchase #7	$243.95	11.270%	$271.4432	$271.44	$271.45	$271.40
7 purchase totals =	$1,047.16		$1,150.4272	$1,150.41	$1,150.45	$1,150.30